The approach shows that the glideslope (if it were working) is a three degree descent angle. You can calculate your own visual descent point (VDP), since one isn't provided for you, by taking the height above touchdown (600 ft. in this case) and dividing it by 300 ft/NM. This gives you 2.0 miles from the runway. Since the chart shows the runway threshold at 0.2 DME, your VDP will be at 2.2 DME.
Assuming that your navigation equipment does not provide a pseudo-glideslope, your best bet is to descend at your normal rate (in a light airplane I would say 800-900 fpm) until you level at 660 ft. (the MDA), then fly to your calculated VDP (2.2 DME) and if you have the required visual cues then descend to the runway knowing that it will be a standard 3 degree descent (300 ft./NM). If you don't have it at this point, then you can start an early climb and fly the missed approach.
Put another way, first you calculate your VDP:
$$\frac{Height~Above~Touchdown}{Descent~Rate}=VDP~Distance~From~Runway$$
$$\frac{600ft}{300 ft/NM}=2.0NM$$
$$VDP=Runway~Threshold+VDP~Distance~From~Runway$$
$$0.2DME+2.0NM=2.2 DME$$
Then you fly the approach:
- Cross HERNY at 2,000 ft.
- Descend to minimums (660 ft.) at 800-900 fpm.
- Fly to 2.2 DME at 660 ft.
- At 2.2 DME, if you see the runway environment, start your descent and land
- If you don't see the runway, start your climb and fly the published missed approach
