i dont think you have to drop the subframe, but the main ARB bracket where the D bushes are are mounted on top of the subframe and bolt through the bottom, a little blindly i might add, you have to peep through holes in the very bottom surface of the subframe to see the bolt heads underneath the top surface of the subframe, 2 per bracket, so 4 in all, and they are located about 5/6" toward the middle from the inner wheel arch.
so raise car, front wheels off, arb drop links off the arb, under the car, undoe the D bracket bolts, and i believe it should extract out one side or the other with a little coaxing and twisting, either side, same obstacles i think, but not too bad i suspsect.
i was about to do mine until i found the source of an annoying noise elsewhere but looking into it, it doesn't appear to be too difficult, and no special tools required, average socket set, and maybe a thin open 17mm spanner or (i think) a 5mm allen key (depending on which arb drop links have been fitted) to hold the knuckle in place whilst you undoe the lock nut. I say thin spanner because theres little room for the spanner on the flats of the knuckle between the arb metalwork and the rubber gaitor that you don't want to butcher.
unless anyone knows otherwise, quite diy'able i think.