This probably equally applies to IFR flight plans, but the general question is can arbitrary (unrelated to an airway or named fix) GPS coordinates be used in the route on a flight plan?
The AIM specifies how flight plans should be filled out, block 8 contains the route of flight:
- Block 8. Define the route of flight by using NAVAID identifier codes and airways
It is possible to do this if you can fly at or above FL390, since you need to get through class A airspace to get to FL390 you can not get to FL390 on a VFR flight plan alone.
Pilots of aircraft equipped with latitude/ longitude coordinate navigation capability, independent of VOR/TACAN references, may file for random RNAV routes at and above FL 390 within the conterminous U.S. using the following procedures.
Define the route of flight after the departure fix, including each intermediate fix (turnpoint) and the arrival fix for the destination airport in terms of latitude/longitude coordinates plotted to the nearest minute