How can you turn the screen off without access to the power button and without using auto-lock?

We are using iPads that are locked down with Guided Access and secured within hard plastic mounts screwed down onto a countertop. We can press the home button with a paperclip, but that's it. We don't want to use auto-lock because there might be several hours where the terminals aren't used, but we don't want them to go to sleep during business hours, otherwise we'll have to grab a paper clip and turn them back on. Also, if we set the auto-lock to several hours, then the iPads wouldn't be off for very long at night. I want to turn them off when we close at night, but it's challenging to open the cases and lift the iPads out, so that's not a reasonable option.

Any thoughts?