Sorry, I think there is a pair of BT scripts to tether a linux computer to the N900, apply the 'computer' script to the N900 and then engage the tablet's BT tethering app and it should work.
I don't remember where the script is on TMO, though there are several on different linux help sites, if you link it I can help.
You also need to know if your app uses PAN or DUN.