[imp] Marking message "Not Spam" and modifying subject

[Daniel Mayer [COUGA.net]]

Hi,
 
we are using  IMP as Webmail system for our customers (we are an ISP). Spamassassin is tagging our messages in the subject and our customers use ingo/imp for filtering these messages according to the subject tagging in a special folder.
 
If there is a false positive it can be reported as "Not Spam" and is correctly parsed by spamssassin and also put in the inbox again. But the problem is that the subject still contains the *** SPAM *** marking and is therefore sorted out again.
 
My question is if anybody has a solution or an idea on how to modify the subject line out of imp after reporting the message as not being spam. 
 
If there is a smarter way of dealing with the spam filtering issue i would also be happy to hear this.
 
Thanks a lot,
Daniel