Well, I have Jo's old Beseler base, and the eraser works really well on the Unicolor drums that came with it.
I also have a Chromega and a Beseler color drum Both have a round rail that separates the 4x5 or 5x7 sheets, and when doing more than two 4x5 sheets you put two side by side, correct? Both Chromega and Beseler had a little butterfly looking thing that would slide onto the round rail after you inserted two sheets, one on either side of the round rail, all the way to the bottom of the tank. Then the 'butterfly' would slide in until it touched the side of the 4x5 sheets, and then the remaining two sheets before you close up the tank.
I would try to find a piece of fairly stiff, but flexible (without breaking when you bend it) plastic tubing with an inner diameter about the same size as the outer diameter of the round rail. I would then cut a small piece off, about a 1/8inch or so, and cut off about 1/4 of the circumference of the material, so that you could use the rest to clip onto the round rail.
That's all I can think of. Don't know if the eraser will work on these. The erasers Jo gave me for the Unicolor drums work, because those drums have a V-shaped rail instead of a round, and it's easier to 'grip' than the round.
- Thomas