Increase bluetooth range

Hello,

At my work (a school), i have some Macmini in audio visual rack. This racks contains other AV devices and they are usually closed. Keyboard and mouse are in bluetooth and, unfortunately, it's really hard to use them. The rack is at 5m from the desk of the teacher and it's really a big issue.

Is there a way to increase the distance of the signal. With a key ? A wireless repeater ? Or anything like this ? We already buy a USB key without success. It looks like it's not compatible.

Thanks a lot for reading.

gg