You could get one of these
And/Or...
Seeing as you have a 50ft yacht, I am sure you have a tender/dinghy as well? You will also have lots of rope. And I assume you will have at least 2 willing helpers?
So you don't need to do a normal drift launch that someone with only one small fishing boat and a boat driver is forced to do.
Here's how I would do it.
1) Anchor your babe magnet near/slightly upcurrent to where you want to launch (or use sea anchors)
2) pump up kite on the huge deck you have there (I assume lines are already attached )
3) Do your best to confirm that lines are not inverted.
4) Put kite in dinghy with helper 1 sitting on it and securing it tightly from the wind
5) Have helper number 2 slowly pay out the (25m plus) rope attached to the dinghy so it drifts down current with the kite on top. At the same time unwind your lines, keeping them slightly taut (enough to avoid loop knots) and checking them all the way for possible inversion.
6) when the tender is far enough out that the kite lines are unwound, have helper 2 secure the rope, and do a careful check of both steering lines to check no line inversion.
7) When ready to launch, have helper 1 put kite in water leading edge down. in most wind/current combos you can sit on the dive platform with the kite edge down and use the steering line to drift it away from dinghy and confirm that there are no line snags on the dinghy. I would not recommend launching directly from the dinghy as it has lots of things to catch kitelines, and likely as not it will be in a position for a hot launch.
8) jump in and water launch as normal
Obviously careful briefing of kite handling and emergency procedures is required