I had three neons in with my female in a 10g divided in 2, so it was 5g space but 10g water so it could be different. I would think neons would be alright but the problem is they like shoals of six or more, but like I said I had 3 and they seem happy and healthy.
What I would do instead is get 2 or three ghost shrimp, I know your thinkng "ehh shrimp are stupid" but they are lots of fun. I would rather keep my boy Tiny (the shrimp) than my 2 cories or my three neons. The ones at the store dont move much but once you get them settled at hope they are crazy little things. Mine swims with my fish, but can never catch up. And hes fought my betta for food (nicely of course, no damage). They are just lots of fun to watch, cheap, and dont take much room.