I suggest leaving the current divider in there while using the craft mesh/plastic canvas as a double. A lot of reviews about this tank say that the males will eventually find a way over them and attack the other. This tank also has a bow front, which is very difficult (if not impossible) to safely divide in half. I believe this tank also has an insufficient filter for one betta, let alone two.
I offered two choices and you only rejected one, if you can't get an ADDITIONAL tank, then take this one back and get a 5 gallon to split :S.
I wish you luck on your endeavour, regardless