I'm right with you, DS is 10 wks.
When using the sink, I use kind of a modified newborn hold. I put his lower back in my right hand, support his upper back/head with my chest and head. His head usually ends up near my left shoulder. My left hand is under both his legs, so that his right thigh is between my thumb and first finger and his left leg is over my left wrist. Or something like this, he squirms quite a bit prior to going, but this positioning contains the pee since either he ends up sagging into the sink enough to catch the stream or it's deflected off my left palm. We have a big counter that I've converted into the changing area, after he goes I set him down to the left and wash my hands with lots of soap. There's also a large mirror so he loves looking into the mirror while being held over the sink or waiting (of course I have to wash the mirror nearly everyday too). HTH.
FWIW this is my third boy, and I've resigned myself to lots of bathroom cleaning. My 4yo is pretty good, but my independent 2yo who has to do everything "ownself" is about 50/50 getting it all in the toilet. Someday we'll laugh.
If someone has a better tip, I love ideas.