To save myself the trouble later, I am going to lock this now. The answer to the question can be found via searching for guppies in this forum, it's been done. And using your best judgement is also a good guide. Ask yourself these questions
"Is my betta aggressive?"
"Can the guppies fit in his mouth?"
And most importantly..
"Is a two gallon large enough to accomodate the betta AND growing fry?"
I think you'll find the answer in the last question.
The second reason I'm closing this is because I see a dreadful turn happening here. To use fry as feeders, or not to. Personally I do not, but I can assure you that many, many, many people do. My lfs sells guppies as feeders for cripes sake. So, let's just let this drop.