You can do this on lots of aircraft.
As has been stated, you can go through the E&E bay on the B747 just behind the NLG (awful stretch though!), same-same for the BAe146/RJ where it is on the lower stbd side and enters the flight deck. It was the standard way in and out when at an outport with no engineering support, and I've once heard of a couple of undisciplined wags ordering a coffee from the F/A's, and hiding out there with the acft on AP.......
My Dad was on P2 Neptunes, and the
normal way in was through the nosewheel well, there was a narrow catwalk on the port side (And the normal way to his station near the stbd trailing edge was a crawlway over the wing spar). Apparently it was pretty breezy on the flight deck with the gear down.
Cheers