I'm not really that fussed on what this method is, other than that it should somehow set the screen start position to the current mouse position.
In the old editor, this was done by right-clicking at the desired spot, then selecting from a dropdown. This editor uses RMB for mouse scrolling, so that's out of the question, but perhaps a hotkey to place the screen start at the current mouse position?
I noticed when looking through the hotkeys that P + LMB drags the screen start position. Perhaps P + RMB could be "set to current location of cursor"? I wasn't aware of P + LMB when I started writing this topic (I thought "I should check, in case such a thing already exists and I'm just not aware of it"), which does help a lot, but I think being able to directly set it rather than just drag it would be useful too, and not particularly tricky to implement.