Depends on the bi-pod. Some are designed to attach to a Weaver and/or Picatinny rail, some are designed to attach to a sling swivel mounting stud. I have seen some that mount to a rail or swivel stud. They have some kind of adapter that mounts on a rail.
You'll need some sort of forend stock to attach either mounting device. A rail could be JB Welded to the tube I guess. Perhaps an extra wide custom barrel band that a sling swivel stud could be attached to might work too.
I used multiple layers of PVC pipe to build a small forend to mount a Weaver rail on my 2240 carbine.
![[linked image]](http://i79.photobucket.com/albums/j147/airgunandy/2240carbine2.jpg)
I plink, therefore I am.