There's a totally usable, but slow, method for doing this right now. Shift+PageDown+Copy will push down whatever is at the current step to below the inserted steps.
So, say you want row 2 to be your new starting point:
1) Shift+Mark from row 2 to the end of your pattern
2) Shift+Mark to grab that into the buffer
3) Move to step 0
4) Shift+PageDown+Copy will insert the copied rows at step 0, and, will push what was at step 0 and 1 to the end of what you inserted
I also find this SUPER useful to "rotate" FX or Mod stuff.
I'd recommend saving or duplicating the pattern first

as this can sometimes feel a tiny bit fiddly if you've not done it before.