This isn't as impossible as it sounds -- boy, do relays sure come in handy!
Alright -- I need a bigger box at the 2nd location, to begin with. Plastic boxes don't generally have conduit knockouts, so we'll use a metal box here -- a 4 11/16 by 1 1/2" square box with a 1/2" single gang mud ring will do the job in all cases, or I could use a 4" by 1 1/2" square box with a 1/4" single gang mud ring if I had all 14AWG cables. I'll also need to use NM clamps that clamp the cable on the outside of the box as box fill is critical here. Finally, make sure to leave one side of the box completely open, with one of the 1/2" KOs on the ends pried out to fit the relay I'd then put in as the last step before installing the box into place -- I'd use a Functional Devices RIBU1C (Manufacturer specs) here as it's relatively inexpensive, easy to install and wire, and amply rated for the task at hand, as well as being fully UL listed, which most off-the-shelf relays are not.
Once the box/relay combo is installed and mounted, I'd then wire it up -- all grounds go together of course (box pigtail, switch pigtail, and all three cable grounds). From there, the black wire to the outlet goes to the black wire from the first switch as it will become the hot feed later, as well as the yellow wire from the RIBU1C. The blue and orange wires from the relay go to the traveler terminals on the 2nd 3-way switch, while the white neutral wires all nut together along with the white/yellow striped wire from the relay. Finally, the white/black wire from the relay goes to the red incoming wire from the first switch, the white/blue wire from the relay gets capped off with a nut, and the common terminal on the switch goes to the black wire going out to the light.
I'd then button up the first box (carefully, as it'll be quite stuffed) and move onto the other switch box, which needs a trifle bit of rewiring now to make everything work as intended. The wire to the common terminal of the switch gets removed and hooked to a pigtail which goes to the common terminal, and also is attached to the black wire going to the other switch box, which is also disconnected from the switch. The existing white and ground wires are left intact, and the red wire remains hooked to the switch.
Once everything is buttoned up and turned on -- the first switch should turn on and off the relay, which acts as a stand-in for the first switch, only located remotely off in the 2nd box, freeing up one wire to serve as a hot feed while the other switches the relay on and off.
