Sure it can be done,
you just need to have the same condition in the two IF()'s, both
looking at y, and then supplying the x's or y's in the second argument.
This will guarantee arrays of similar length and it will exclude y=0:

=RSQ(IF($J11:$AG11<0,$J11:$AG11), IF($J11:$AG11<0,$J7:$AG7))

(with x's in row 11 and y's in row 7)

Regards,
Kostis