Officially, or unofficially? As a rule government bureaucracy doesn't deal well with informal arrangements between friends, so officially I'm quite sure the FAA answer is no.
It's like asking the IRS if you can pay your neighbor to mow your lawn: The IRS would say yes, but they would expect a taxpayer ID and a cut in the form of taxes. To get that, you'd need a business license, to get that you'd need to show OSHA compliance, and so on, and so forth...
So again no, a pilot cannot "hold out" and charge a fee to perform aircraft maintenance unless they are also an A&P.
However, if you are friends, the preventative maintenance is within the scope of what is authorized for an owner/pilot to perform, and you invite him to your hangar to "help", (while you supervise) nobody will know whether or not you buy him lunch or slip him a crisp $20 for his trouble. Just check the work and know that if the drain plug pops out and your engine seizes in flight that it's on you. No finger pointing allowed.
I am not advocating breaking rules, but when you examine the ethics of a scenario as you have in this case, and you know in your heart of hearts that you are in full compliance with the intent, then don't trouble yourself asking for permission from strangers, or from a bureaucracy intended to safeguard rather than restrict our liberty.
A bureaucrat will almost always take the safe way out and say no, so in these sort of cases I advocate the military's old policy of "don't ask, don't tell".
From a couple of the comments it is apparent that my answer was not interpreted in the manner I intended. The point I was trying to make is, that in matters of regulatory compliance it is important to understand the intent and apply some critical thinking to discern what might be acceptable when you are in a gray area.
To further illustrate let me offer a couple scenarios with a bit more detail –
Scott is a 20 year old who just earned his private pilot’s license. He is trying to build hours towards his commercial, and pumps gas at the local airfield to earn money towards flying. He is a hard worker, loves aviation, and is well liked by the local pilots. Lately he has “casually offered” to change the oil for some of his customers, hinting at an expectation of being paid.
Is this OK? NO! As I indicated above, Scott is holding himself out to perform preventative maintenance functions on aircraft where he is not the owner operator. The regulations are clearly intended to prevent such shade tree mechanics from compromising safety and undercutting licensed A&P mechanics, while still allowing owner/operators to perform routine and minor operations. At no time did I intend to suggest this might be OK, and that “nobody will know...”
Tom is a 70 year old retired engineer and Cessna 172 owner. He is in good health, but less mobile than when he was young, and had a knee replaced last year. Carl is a 35 year old ex-military pilot who is now a first officer for a regional airline. He also owns a 172, and rents a hangar right next to Tom. Over the last year Tom and Carl have become friends, and often swap flying stories and share tools as they do as much work on their planes as allowed.
Carl noticed the last time he watched Tom change his oil that with his replacement knee it was very awkward for him to get down underneath the engine to access the drain plug. “Why don’t you let me help you out there Tom?” Carl casually offers the next time they are changing oil. “I will get that drain plug for you if I can have a cold Coke out of your hangar mini-fridge” he jokes. Tom semi-reluctantly gives in, watches and verifies that Carl did the work correctly, then fetches him a soft drink as he expresses his thanks.
Is this OK? Technically Carl performed maintenance for compensation on an aircraft where he was not the owner/operator, and he is not a licensed A&P mechanic. But really, do you think this is actually the kind of scenario that the FAA is concerned with preventing? Don’t you think they might have bigger fish to fry?
Tom could have refused the offer. Or he could have written a letter to the FSDO, or AMDO requesting permission. Or he could have gone on the internet and asked random strangers what he should do.
But if I was Tom, or Carl, I would simply do it and not lose a minute of sleep wondering if the FAA will find out and I might go to jail for displeasing my government. No ethical dilemma or safety concerns here, the intent is met, but maybe that’s just me...