Recently I got a vintage Schwinn exercise bike and rediscovered that time slows incredibly when watching the timer, even with the radio on. So I built and installed a simple book shelf for the handle bars.
The scrap of plywood is bolted to two smallish L braces which in turn are clamped to the handle bars with hose clamps. It's easy and requires no permanent modifications that might degrade the bike's collectability. LOL Just kidding; you can barely give these things away anymore.
Scrap of rubbery drawer liner keeps my book from sliding off. Now I can read and pedal until either 1) the timer sounds or 2) my rear goes numb. When it's the second event (which it usually is now that I'm building up a tiny bit of stamina), I get off the bike, march around for a minute, and get back on.
I'm exploring options and experimenting with available materials to prevent NBS (Numb Butt Syndrome). I'll report if I find a solution that doesn't involve temporary dismounts!