Length of txt records

To all,

I didn't see this in the FAQ, nor did I see a good answer.

Some companies have lots of remote offices which users can send mail from.
We have plenty of domains that have more IP's than can fit in a 255-char TXT
record.

Suppose I've got 30 "valid relay" IP's to list.  What's the best way to
construct a "large" SPF record?  Can you have multiple TXT's?  Can you have

- Erik