Okay, the idea is similar to Speffz. You have 12 faces and 5 locations on each face, but the locations are defined in a way that makes it relatively easy to keep track of. Every orbit fits into the 60 locations in a roughly similar way. You obviously can't use single letters for this, but you *could* use uppercase letters + lowercase letters + 1-8, or numbers 1-60 (benefit: easy to divide by 5 to figure out the face/location number), or syllables (12 consonants and 5 vowels), or just sixty random images. It may be a little trickier to keep track of which pieces have been used, but if you are considering a Mega-/Master Kilo-/Giga-minx BLD you will probably have no trouble.
The locations on each face are arranged like so:
For the 8 faces around the "equator" that I didn't label, just proceed in a y-erly direction around the puzzle, numbering the locations on that face in the same way you did the labeled one. It's your choice on how to order the faces but I suggest U=1, then 2-6, then 7-11, then D=12.
Having things more or less symmetrical around a y rotation should help a bit with spatially imagining where the pieces are... remember that you're probably going to have to come up with pure sticker commutators on the fly, so it'll be useful to be able to say "okay, location 3 on face 4 is just a y2 over from location 3 on face 2, which is right in front of me".