Catching up Production from Warm Standby after maintenance - Please help

Hello All -

I will soon be receiving a new production and warm-standby machine.  Prior to now, we have only had one database machine and no warm standby. 

We had planned to feed the standby with one backup and then use WAL files rsync'd over until either catastrophe or maintenance required on the primary machine.  I will be able to properly close out my users on the primary, force a closeout of the log file (pg_switch_xlog), and shut it down.  Then I can catch up and ingest the last WAL on my warm standby, let the users in, and have the warm standby become the new primary.  All okay so far.

But.  When the primary is vacuumed, re-indexed and all clean and shiny again, HOW do I catch up with data changes that happened in the meantime on my warm standby without corruption or >30 minutes of user down-time?  I cannot re-ingest WALs from the warm standby into the cleaned up primary or I get a PANIC, and I don't have time to run a full backup on the warm standby and ingest it into the primary leaving everything down. 

I know some of you must have tackled this before, so I am really hoping you can help me.  I checked the archives but didn't see anything about how to recover the primary after the repair or maintenance had been completed.  I was really hoping to use the logs on the warm standby to feed into the cleaned up primary to catch up, but it seems that's a hopeless idea since any vacuuming or other cleaning I may do changes my binary data files beyond the WAL's recognition.   

Thanks in advance for your assistance. 

Best regards,
Jennifer Spencer