Well subfolders are not workable in IMAP either, so you have few options. One solution, you need the subfolders, set up the Personal BES. Also, for about $10 bucks a month you can setup BES hosting with a variety of companies, recommend mailstreet.com, but if you do a search on google with words "BES hosting" you will find multiple lists. Obviously both of these cost money whether be hardware costs or the hosting costs...
As an "free" alternative that I use, I use Opera Mini on my BB and browse to my email provider email site and use it that way. Security reasons, never gets downloaded to the BB device, stays on the email provider's website and I can use subfolders, send email, etc...as if I was browsing on my PC. This options works well for me.
