Ive just finished wiring up my sub and amp into my mk2 ph1! have you sorted it yet? maybe I can offer a few tips?!
About the bonnet realease gromit its a small round one you can see it if you look behind and below the water tank, heres how I did it...
I pushed the gromit through from inside behind the glove box, so its loose on the bonnet release cable.
I attached some thread/string the power cable and tied it tight enough not to come off
I used a screw driver to help push/feed the thread slightly through the gromit hole and the screw driver wedged in the process, holdng it in place.
I then went inside and pulled the thread through far enough so it wouldnt pop back out when i removed the screw driver
Then pulled the thread and power cable through.
No need to remove the little fuse box attached to the wire!
Job done!
As you said you had it wired up already so im sure youll be fine,
For tidying up I used a screw driver to help push wires underneath the door trims!
Hope that helps!
Peace