I know it's kinda cheating, but I usually order a side, like a baked potato and an iced tea. I have them bring out the potato as my main course. I like marinara on it (instead of butter or sour cream). Or I will use a teeny bit of butter and some steak sauce on it.
I eat a protein bar right before going in, so I'm not really super hungry.
Even in the most expensive places, a potato and drink is going to only be about $10 with tax and tip. Alot of places have a decent sized, side salad and you could do that with that too.
I would leave slightly early, taking the initiative to pay the waiter first and not become part of the assumed split group. One thing I will say, it might be easier for me, because I don't drink, so my friends already know that I'm not part of their 'go to the bar and split it' groups.
Honestly, just tell your friends your watching your alcohol right now (you don't have to talk about losing weight) and tell them you won't be part of the split check group for the next little bit. One thing to consider, is that if you are uncomfortable with the 'split' thing, there are probably several other girls that are uncomfortable with it too. In those types of things, it's almost always one or two girls that push for it because they are the ones that run the tab up.
They just need a leader to help break that up. You will be helping others to stand up for themselves too.

