I made a 1024 bit key and it produced a record for bind that looks like the following:
label._domainkey IN TXT "v=DKIM1; ... a whole bunch of stuff for a total of 321 characters"
Well, bind has a hard limit of 255 characters per line, so you need to detect that and split it the way that bind wants it to be split.
It coudl be a FAQ entry:
Q: I created a new, longer DKIM record of 1024 bits (or more) and now bind won't load the record saying "ran out of space".
A: The record must be split into one or more parts so that no part by itself has more than 255 characters. See https://lists.isc.org/pipermail/bind-users/2008-May/070204.html for a description, see http://www.virtualmin.com/node/15907 for quick fix.
Example: label._domainkey IN TXT "v=DKIM1; first 200 chars" "next 200 chars" "etc..end of record"