Best practice for shared laptops used for presentations

Hi,

We have several laptops we loan out to users for presentational purposes, powerpoint mostly. Typically the laptops are loaned out for a day or so.

We have 100 users who potentially could loan out any of these laptops

It is obviously not feasible to add all users to all laptops..... and the laptops must be encrypted and POA invoked.

Given this scenario what would be best practice in terms of adding users to the laptop, given a days notice?

I really want to lessen the burden on the helpdesk too if possible.

Thanks