i do have a tow bar though.... maybe lock in the hubs and leave the driveshafts out and pull it around for 500 miles? lol
I know you were probly just joking but this method won't do what your after, you'll need to drive the gears to heat them up to break them in, coasting I don't think would heat them up properly and not to mention coasting would be pressure on the coast side of the gear not the drive side..
Best bet is to trailer it to an FSR or long smooth dirt road somewhere. You don't have to do all 500miles (800kms) in 1 go, you just need to take it easy for the first 500miles (800kms), that's why I suggest a dirt road and not a trail, lol, unless your really good at taking it easy..... OR if you know someone that's trust worthy with a Toy that can use the 2 totally different drop outs for a couple weeks of road use. I know you have LC and p/u drop outs so this may be difficult. Or if your careful you can go wheeling to break them in just take it easy, like do only 31" tire trails, lol, in 4wd so both diffs are being broke in at the same rate.
When I set up my buddies v6 8" 5.29's for his not road legal Toy p/u wheeler, we installed each in the rear diff of his wife's 93runner to break em in, he drove it to and from work for a couple months to get enough miles on them. The 5 sp and 31's sucked ass he said tho with the 5.29, felt like a power house even taking it easy but reved out before hitting highway speeds, lol. Almost like he was in low range he said, haha. Nice part was we were still building his rig at that point so it wasn't like the drop outs needed to be installed in it yet anyways.
When we did my Zooky buddies set, he bought spools for both drop outs so we went for several long drives down a close by forest service road (FSR) in rear wheel drive and then once it was broke in we swapped drop outs front to rear and repeat, took a few weekends and a lot of beer, er I mean fuel but it worked out. lol.
This is something I'll need to consider as well, since my Rover isn't street legal either, once I install the brand new 5.29's I'll need to do break in somehow too. More than likely I'll just take it wheeling and take it real easy for the first month or 2, no foot to the floor stuff or bouncing and spinning, the rest should be not much different than on road driving really.
Are you going to be setting them up yourself?