You can try gluing a center fin and you'll surely get a ton of upwind performance.
If you're in Europe, Decathlon have a basic slide&click one, 20€ for a set with the base. Glue not included, you can use that provided in the board repair kit.
A much better option is a JP spare fin with a US box base, bur not easy to find and will cost 1/3 of that board.
Slingshot stick-on center fin is huuuge (pretty much a keel) and although not meant for inflatable boards, some have tried it already and it works.
Drop me a PM if you need more info