Exclude keynote users (no replies)

Is there way to Exclude keynote users from PiWik? Best practice suggested by keynote is to use user agent filtering as follows.

Transaction Perspective Agents can be filtered by using the keyword KTXN, which is a part of the following Transaction
agent string:

"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; KTXN)"

Application Perspective agents use this string:

"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 4.0; KHTE)"

If this is not supported in PiWik, is there a way to clean the data from database directly for these users?

Thanks