ok, here's what I'm about to try next; I'm gonna put on my workout clothes, get my shoes on, get my headphones in, and inject around the place where my outer leg meets my outer butt. Then I'm gonna IMMEDIATELY go for a brisk, three mile-walk. I've walked around my house with my hand on the area where I'm gonna do it, and can confirm that area is in constant motion when I'm walking. I think this might work to prevent the soreness and the welt because when I DO have soreness, exercise makes it stop being sore for awhile; maybe the walking and the constant movement of the area will help disperse it.
If it works, I'll have a bonus of incentive to exercise every day! Here we go!
Update: Ok, 3.44 miles in one hour and three minutes. Including the time in case anyone later decides to try this (I won't know for until tomorrow morning if it worked) but is at a different fitness level from me.
Second update: It's been sixteen hours. My butt still hurts, but I don't seem to have a bruise. Maybe. I don't know; I injected in a spot that is unfortunately very difficult for me to SEE. I went and got a hand mirror and bent over and futzed around, then my perimenopausal vertigo hit and I lost interest in the project. But I'm going to do it again tonight, on the other side, in a place that still moves plenty when I walk but is easier for me to see.