You'll have to experiment!
...
I'd try putting the NB & GPU parallel after the CPU, then join them again before the rad. use oversize Y's though, 1/2inch Y's have an inner diametre of 9.5mm!!, a 14mm~5/8" Y has 11.5mm inner.
............----GPU---
CPU---<..............>---RAD
............----NB-----
If it comes out right , like the above,**EDIT** ignore the(.......) dots, they're for spacing cause normal gaps don't work :shrug: ...