Replacing $sth

[Henri Asseily]

I'm trying to do the following, and was wondering where I should look 
to get a good handle on what's going on:

I have an $sth that's pointing to a dead server.
I have a new $sth2 that's pointing to a good server.
upon the user doing $sth->execute, I want to be able to get $sth 
pointing to $sth2, effectively making $sth valid again.

I understand that $sth is a tied hash. Can it be cleanly untied and 
retied to what $sth2 is tied to? Would that do what I'm looking to do?
I have no problem coding up some C, as long as I can be pointed at the 
relevant code in dbi.

Thanks.
H.