I don't use my 3-roll tank with one roll any differently than my 2-roll with one roll. It works fine. The air bells are not really a massive problem.

Use what you have, and get a 2-roll tank later when your money permits. As a bonus, that will let you do up to five rolls of 35mm in one big developing session. Then blow your mind by adding the 5- and 8-reel tanks!

(I have one of each of these four, and there are times that they all get used... about once a year I have a massive backlog of film to catch up on, and having the assortment of tanks is really convenient.)