<How would you suggest force feeding him as he is very delicate and I can't picture him being able to swallow.
The vet also gave a soft plastic tip syringe for administration directly into his mouth. >

Use mushed legless , headless crickets and put them into the syringe mixed w/ the flagyl so that you don't have to 'pry' his mouth open twice.
Very gently pry his little 'lips' open .....not the very corner but off center
Hold him wrapped him in damp paper towels when you do this /otherwise you could scrape his skin

Kimmy, very important......... do you see him shed ? When on medicine... he will shed more often. Get he food and flagyl ready and squish it into his mouth when he 'yawns' during a shed. This works like a charm. I did this for 7 weeks every time my black eyed tree frog shed. I waited around after the light s went out. They will typically shed as soon as they wake up at nights ( after lights out ). Practice handling your syringe ie filling it and see how fast the mixture comes out. I would suggest use the bodies of 2 small crickets and mush w/ the flagyl. You will want to keep amount you are pushing in as small as possible and on the thicker side so he does not choke. He will take care of swallowing. There increased chance of choking if it is very watery.

Can you please post a photo of that syringe?

Heat....careful. How about putting a thermometer right in there next to him.. You don't want to overheat him? He does not need extra heat.

Lynn