The code to resolve the TracLinks to full HTML href's ('attachment:file' to '/attachment/wiki/foobar/file') needed by the flash plugin is at the moment self written.
Every TracHacks macro seem to re-write its own implementation, while this is actual a basic functionality which should be provided by the Trac API itself.
I opened a Trac ticket to request this, ticket:7728, and also found an appropriate solution which uses the Trac wiki engine to resolve the TracLinks. Please have a look on the ticket attachment. The code could be easily taken over to the FreemindMacro and would !add complete, fully working support of all current and future TracLinks.