Actually kit lens can still work. I do not use f2.8 even when I have a 2.8 lens because I want DoF to be deeper so I can capture more people at the table in focus. I will use 5.6 or larger. So the key is your shutter speed and ISO and your flash compensation.
Method 1
What you need to do is to use M mode, a little trail and error (that is why photographer have to be at the even early). I start off with 1/20s in exposure, aperture 5.6, ISO 800 if it is quite dark. I will set the flash to bounce (even if ceiling is not white) with a bounce card (I use demb) to send some white light forward. I will also set flash compensation to -0.3. I will test shoot and adjust till I get a favorable lighting effect.
Method 2
I will use A mode. Same testing SOP. Start from F5.6 S will default Shutter speed to 1/60s in low light (in D90). Adjust ISO and Flash compensation till get desired effect.
This is an example of my test shoot. This one is at F2.8 though.
A mode, 1/60s, F2.8, ISO 800, Flash compensation -0.7
After that, when doing the actual shooting, I will be able to adjust my aperture to get DoF I need for specific effect.
One of the result. Don't have permission to post the rest.
A mode, 1/60s, F5, ISO 800, Flash compensation -0.3