You would have to start with a blank nozzle. You cannot simply put more holes in the existing one and retain much confidence in it structurally.
And when you think about jacking up the ICP
for milage, remember that the pressure comes at a cost too. Parasitic drag on the camshaft/crankshaft. I have done testing running ICP
up to some serious heights while coasting and it will damn near put you into the steering wheel at 3800psi. That's right. The drag from the pumps damn near slides the back tires...
In terms of milage, you don't need a second pump anyway. When at crusing speeds you're not coming anywhere close to emptying the injectors, so even a piss-poor stock pump can run whatever pressure you want. If you want to try a little more ICP
when crusing, just ask for it. Or get a resistor mod of your choice if you want to change it on the fly. But regardless. You don't need two pumps to run high ICP
when just cruising if you wanted to.
And your stock nozzle is a 7 hole as Jim said. Going to a DT466 nozzle is not likely going to yeild better efficiency.