I wish I had a great answer for you, and this is a real problem if your gym is crowded. Lacking a magic-wand solution (or installing a treadwall in a private space) here are some options:
1) Try to do outside on the weekends, again going early/late to minimize conflicts. You’ll need a like-minded partner. This isn’t ideal since you should be doing these sessions multiple times per week.
2) Bouldering up and down routes, of course this has to be continuous and depending on the layout of the gym’s bouldering area may or may not be feasible. This has the advantage that you’re moving all the time and so you don’t necessarily dominate one problem. The hard part here is that you have to keep the problems easy enough that you can stay on the wall. I have a treadwall and a moonboard in my garage; a luxury, I know. But the treadwall is perfect for this. And when it gets too boring, I do use the moonboard, sticking to easy problems, dropping off and getting back on quickly and repeating the same problem multiple times, usually at least 4 times, sometimes 10. The problem is I get fatigued on that specific range of motion the problem requires, so it’s better to switch to another problem quickly. obvously a moonboard with the LED lights in key for this.
We haven’t received any hate-mail from climbing gym managers yet but I’m sure it’s only a matter of time!