Using pg_migrator to upgrade 8.3->8.4

We are looking to upgrade out 8.3 db to 8.4.  The full dump and
restore is not very attractive due to the downtime involved.

pg_migrator is an attractive option, but we have butted up again the
integer datetime timestamp problem:

"Old and new pg_controldata date/time storage types do not match.

You will need to rebuild the new server with configure
--disable-integer-datetimes or get server binaries built
with those options."

We also noticed that the are non id rpms available for 8.3, but we
couldn't find any for 8.4 here:
https://projects.commandprompt.com/public/pgcore

So, is the best option to compile postgres from source?  Is there
anyway to change the storage of timestamps in our 8.3 db online (I am
guessing no...)?

Mostly I just need a sanity check before I waste a bunch of time :)