This would probably be easy to do if you set them up as external users. In my screen shot, you can see I have multiple groups. If I have them switched on, they are counting as a license. When I switch them off, the seat is not counted. Their account info and progress stays, they are just unable to login.
The fee is being paid by you, the organization, unless you are then collecting that from the learner yourself. For example, if you have 100 people that need training and you bought 20 seats, you could put them into 5 groups, and rotate which group is turned on.