Different kites are more stable than others in this kind of launch. In gusty winds mine will hop and try to launch forward. Others will fall back. A buddy can leave his and go for a snack, just sits there all day.
Mine was hopping like crazy yesterday in gusty 20-25kt with an 8m. I ended up using 2 bags, 1 near leading edge, 1 near wing tip. Had to pull pretty hard on top line to shake them off. Make sure bags are slippery material.
Usually you want kite at least 3/4 depowered, with bar all the way out.
As you walk back run your hand on top FLYING line. (to reach top line, grab canopy lines and pull down until you reach it). You can pull on that line to keep kite from hopping, falling back, or taking off. (NOT steering line!!!!! a buddy got this mixed up....and had some spectacular launch fails)
This may be controversial, but I think carabiner self launch is one place where it is ok to get a civilian passerby to help...put it in launch position, make sure stable, then "just hold this kite in place, let go when I tell you"...I give a little training on how to stay safe, only hold leading edge, do not touch any lines, just let go if you feel unsafe, where to move to get to safety, etc.
Our kiter buddies also help each other in iffy self launch situations, one launches, then holds down the other kite in self launch position with their kite in the air...I hate doing this, feels very sketchy.
Look up the Flysurfer Cronix self launch tool....i am thinking of adding something similar. ...tie bottom third of kite to a heavy object in front so it can't jump up or back. Attach a leash with a pull release to the connection. Once you are clipped in and ready to go, pull the line to release the tether, up the kite goes. It would be a pretty easy DIY project I think. Or arrive with friends and rig quickest, so you always get a launch.