If sudo or fstab won't help, you are probably at the point of having to make a special group, whose purpose it is to run that script/device. Then add that group to allowed users.

This is from memory, but I'm sure Ubuntu allows it's users to run mount via sudo

sudo mount -t ext4 ....etc,etc
[download]

so I don't think any sort of filesystem permission checking stops mount by non-root users. Ubuntu may even have a group called mount. ?