Hi, lala. Welcome to ETO
The transformer inside a disposable camera is no where near enough to jump a 1-2cm gap. Using a basic rule of thumb (1kv/1mm, or 10kv/1cm), that would require 10-20 thousand volts. The transformer inside the camera is usually about 300 volts on the output. To get 20kv from two AA batteries, you would need a transformer with about a 1:6666 turn ratio, and to fit it in such a small space the coils would have to be absolutely tiny. This means a lot of resistance, and things just wouldn't work out right. I'm afraid what you are suggesting would be very difficult, unless you use a transformer output to feed another transformer, etc. It would get very complicated. Are you sure you can't adjust your space requirements? We could work with you a bit easier if you increased the space to, say, 3cm x 5cm. Is there any chance of this happening?
Der Strom