Wait...so you stand on the side step pad of the trailer and then operate the throttle to back it off?

? Nobody in the boat?

? That's got disaster written all over it if you aren't careful.
Why can't you get the trailer any deeper? Are you at the end of the ramp? The ramp too steep or the water is just too shallow to get any deeper?
We had low water levels here for several years. I experienced having to get out and lift up on the ski platform and walk the boat to deep enough water. We're talking water less than a foot deep (making sure that you shut the engine off before anything gets sucked into the RW pickup). I've had to bring a shovel and wade out to the power loading hump (that builds up 15' behind the ramp) and knock it down before I could launch and then again before I could load. I've had to back the trailer so far into shallow water that the front wheels of my truck were in the lake. I've been on ramps that were so steep or just so s*****y if you didn't have 4WD you couldn't use them. I've had to be creative more than a couple times but I never had to stand on the trailer to off load the boat. The last straw is when you run out of ramp. If you get the trailer tires to the very last edge of the ramp and you still aren't deep enough to float the boat, you're pretty much screwed. You either find another spot or you didn't ski. Plain and simple.
The latter definitely sucks but when you:
A) Drop the trailer wheels off the end of a ramp or
B) Ground the boat in shallow water or
C) Make a trip to the hospital by improperly powering the boat off the trailer
I can pretty much guaranty that you won't be doing anything like that again.