Just got it done on Friday and it was not difficult with some planning (thanks to SB for that tip!). Remember there is no time limit so take your time and stay calm.
The night before, I swapped my octo for a standard 2nd stage on a longish octo hose (40") and we used that to buddy breathe from. My normal octo (a sherwood minimus) is downtuned to keep it from freeflowing (like many secondary 2nd's are) and as such, it can be a bit difficult to pull air from. Also, since it's low profile, the purge button can be "difficult" to reach as it's different. I figured a standard easy to breathe 2nd with the standard round purge button in the middle made for one less thing to think about and fiddle with. Having the longish octo hose gave us a little more room to move around.
Since it said "exchange gear with a buddy" we interpreted that to mean that we're a buddy team and as such we're there to help each other out and lend assistance as needed.
We decided ahead of time 3 - 4 breaths before passing the reg back and that the person with the reg was the one doing work (doffing or donning gear) while the other person remained calm and just kept the first at hand so we didn't get separated (holding on to a shoulder strap). If the reg-less diver needed air sooner it was just a matter of getting the other's attention (a pat on the head or shoulder) and signaling for the air.
We decided on a sequence: one fin, other fin, SCUBA unit and finally mask. Mask was last because my buddy was worried about the saltwater burning in his eyes.
We also decided not to unclip BC or fin straps, just loosen them all the way. That way the recipient didn't have to fiddle with clipping things back up while donning.
We also decided that nothing gets handed over until the other person is at the same stage and we're both ready. For example, diver 1 removes ONE fin and then gives the reg to diver 2 to do the same. We then breathed a round calmly while handing over the removed fins. Then diver 1 proceeded to don the fin while diver 2 waited as before. After 3 breaths the diver donning the fin would stop and get ready to give the reg back so that the other diver could get some air. If the fin was not yet on, diver 2 (who now has the reg) would lend a hand and help get diver 1's fin secure. After we both had exchanged one fin we proceeded with the other and then the rest one step at a time, lending a hand as necesary and respecting the breathing rotation.
My buddy's BC was way too big on me, so we decided to start out with the BC's swapped. I had to hold the cumberbund closed with my hand or keep my elbows pressed against my ribs in order to keep it on until I got my BC back. Also it was much more floaty than mine so I was slightly positive (even with 2 kg extra lead) until I got my BC back. In retrospect I'd have done a weight check before dropping down swapped that out first.
We did get it done on the first attempt and the instructor gave us both 5's. His main comments were that we planned it out exceptionally, remained calm and got through it as if it were easy. He commented on my being underweighted, but since I kept it under control it wasn't an issue. He was also very happy to see us work it through together and help each other out during the task (helping tightening down or untwisting straps, securing the primary second from getting rapped in the BC, etc). He mentioned that in the past the DMC's he's worked with had tended to be very "every man for himself" not helping out and practically yanking the reg from each other's mouths.