I have thought about this, and tried a few things out, just in case they worked, and they didn't.
I can't see a way to achieve this, and here's why...
Expressions can only work on the tags or file status, for any given single file. There is no way to assign value X to file A, then go to file B and say "make value X equal the same as file A plus one.
There's no way to reference the sequence number from a playlist, not even in the playlist itself viewed as album thumbnails.
I thought we might get somewhere with listitem(), but in order for that to be any use, we first have to force all of the album values present in the dynamic list into a single field that is applied to every file in the list, in the order that they appear in the list. I was not able to make that happen.
I tried some fancy math stuff based off the track # field, but that failed too.
Sorry saucepan, but unless someone else can see a different angle of attack for this one, I have to say it's not achievable. rick.ca recently came up with a neat keywords solution that I hadn't seen, proof there that he sees other angles for stuff, but not this one.
The playing field for expressions is massive, really, really, massive, but it does have boundaries. I think you will have to accept that you have reached a boundary with this one.
Regards,
-marko