Move the skimmer to the left as far as possible and ad a new baffle at the place where there looks to be a brace along the bottom. Then add LR rubble in the far right hand area where water is dumped in and add chaeto to the new chamber between it and the skimmer chamber. It involves a bit of work, but it's the best solution I can come up with. And make sure you still have enough room in there for all the siphon overflow you get when the return pump shuts off.
C.Eymann is right, a very small fuge is almost not worth the effort if it's for nitrate removal. But if it's to grow pods for the system, it can work and it isn't a big job to maintain.