I have classic Kreitler rollers. Being a wood worker with lots of odd bits of pine around, I "banged together" a pair of boxes about 3" wide, 12" long and just below pedal height when the bike is on the rollers. The pedals are an inch or so above these blocks when I'm under way. I then cut a board wide enough to hold those boxes/blocks and long enough to place those two blocks where I wanted them, securely. I drilled two holes to capture the center two legs of the rollers frame so this mounting block cannot slide out of place. Easy and very effective. Light and easy to set up, take down and move around.
I don't go "clipless" when on the rollers so I don't worry about the cleats sliding on the blocks nor on the concrete floor. Easy to start and stop each session.
