Hopefully the gasser has multiple burners with controls for each?  On a newer Weber for instance, it has 3 burners - left, middle and right.  I would turn on either left or right and leave the other two off.  That way you can still do indirect heat.  Then take the grate off above that burner that's on and put a foil pack full of wood chips on it.  It's not the same as a real smoker but it'll at least give you some smoke flavor.  When you're making the foil pouch poke random holes in it for the smoke to escape.

The chips won't last real long so you'll need to refill if you want more smoke.  It's not going to be nice blue smoke, though, so 1 pouch is probably going to be enough for ribs. 

I'd curl them like people do with a mini.  Then use only one of the burners to create indirect heat.  Put some wood chips in a heavy duty foil loaf pan for smoke.  Rotate them around to prevent burning.  After a couple hours, I'd unroll them and grill them on low heat flipping every 5 minutes to prevent burning.  After a couple flips, start mopping with sauce, flipping as needed to prevent burning, while it cooks the sauce onto the ribs. 

They won't be fall off the bone, but if you put in some prep time upfront and trim away a lot of the fat before cooking, they'll be pretty good. 

Can you pre-cook them on the egg and simply reheat on the gasser?

How many racks are you doing? I would use the light one side technique and stack the ribs on top of each other then rotate them every half hour until you think they are ready to finish. Then lay them individually on the non lit side and sauce if desired.

I've frozen almost totally cooked ribs and finished on the egg at a later date with great results, so maybe try just reheating on the gasser. I couldn't tell the difference and no one else knew anything.