This seems to be a learned technique, to put it mildly. :)
After untold failed attempts, I finally landed on a means of re-entering the raft in deep water where there's no means of pushing off the bottom of the creekbed, lake, etc. Would be interesting to hear of others' experiences in these circumstances / other techniques / and what factor might body weight & strength play? (200 lbs here, average)
This technique assumes a port-side re-entry of an upright Alpacka, ie, the "velcro" side of a spray-decked model.
1) Place paddle across the bow and behind any lashed cargo
2) Place left hand on center of paddle shaft, right hand atop near raft tube by seat
4) Orient your legs in the water at a ~45 degree angle away from the boat, and kick kick kick in quick bursts, lifting your torso out of the water and over the boat. Don't apply much hand/arm downward force at this point.
5) Quickly extend left arm & hand out over the far side of raft tube while moving right hand down to the floor of the raft and against the inside tube.
6) The raft will want to flip over toward you as you now apply downward/inward gripping force with hands/arms. Resist this with all of your effort, more kicking, and a lateral, "crawling" body movement across the top of the boat rather than vertical.
7) Flop and flip! Flop your torso, belly-down, atop the raft, and, center of gravity now over the boat, flip forward onto your butt, legs now dangling off the left tube.
8) Pull legs into the boat and take a nice, long, heart-calming break.
I find it amazing how quickly my pulse accelerates during these maneuvers, typically from 70-80bpm up to 150 in just a few seconds. Again, body weight could be a disadvantage in my case. Re-entry in shallower water is infinitely easier, since one can jettison off the bottom in those cases. But simply knowing I now have the capability to get back into the boat in any depth of water is worth all the sore muscles of practice.