I have seen them done two hooks,cable tied underneath...not off the back...you have plenty of options

1.use standard trebles if you plan to keep the fish

2.use barbless trebles...they are easy to remove from the fish...do less damage and easier to remove from your body if you were to hook up! Ouch...I sell these on trade me under the same handle.fish dropping hooks is very low...especially if you keep a tight line.

3.crush the barbs on standard trebles but they can still stick when trying to remove and dont slide out as easy as barbless(not available in nz)

4.Baker method(i believe its called)....8/0 of the back and two 10/0 underneath(opposing with cable tie).Depends on size of popper.

5.use an assist rig from the tie on point at front of popper.That trails down around belly.

It also depends on your popper...some poppers work better with trebs...some you could fish just one treble off the back...match the trebles to the lure...too big and it will ruin the action of the lure.

Hope this helps