Timemachine multiple passwords

Question

I have several standard user accounts on a Mac OS computer.

I have setup a timemachine backup. This backup is protected by a password. So files are encrypted on the external backup drive.

Each user can launch the backup. But he needs to know the Time Machine password.

If a user knows the timemachine password, he can other user's files on the external drive.

I want to prevent that:

• Is there a way to launch a backup without knowing the timemachine password ? (and be sure users cannot read files on the timemachine external drive)
• Or is there a way to set different timemachine password/encryption keys for each users ? At this time, the timemachine password is a "per drive" password. I would like a "per user" timemachine password.

Is there a way to do that ? Or are there alternatives ?

Thanks a lot