I have a Saunders Color Proofing Easel which puts four 4x5 prints on an 8x10 sheet. It permits you to expose each individually through a window mask, and then move the paper so the next section of the paper is exposed.

A standard, small easel and some masking paper makes it easy to expose two prints on a 5 x 8 sheet of paper - one on each end.

I think it was Saunders who also made a more complex proofing printer that permitted exposing multiple wallet size images sequentially on the same sheet of paper.

One caution - if you intend to expose multiple prints and then batch process them somewhat later. It would be wise to leave a little more time (2 or 3 minutes?) between exposing and developing your tests. That will help minimize the latency effect that results from having differing delay times between exposing and developing your multiple prints.