@tanago: If you use the mon0 way on the n900 and connect the wlan0 to an AP on eg channel 1, it locks mon0 automatically to channel 1 too
If you like coding and have the time, you can edit the clevenHelper.sh file as root to do this. Check lines 51 to 54. I'm guessing this is the part you need to modify as well as replace all references of wlan0 with mon0 in the rest of this bash script. I cannot really promise, but if you give me complete instructions on how to enable monitor/managed modes then I might give you a test version to test.