I am not an expert, but I think I followed the same path as you. Here is the solution that works for me, which is only slightly different from the last thing you tried:

$dbh->do(" SET_CLIENT_ENCODING = 'Latin1' ");
[download]

I'm not sure that using '=' instead of 'TO' matters or not, but this did work for me.

HTH

Update: Fixed typo (forgot 'do' in code).