There is no concept of subscription for conversations except for being notified you received one. You also would be better off using a Telligent job versus a windows service because you would then have access to the in-process API which has some exposure of conversations. There is also some events available you could consume in a CSModule to trigger that a conversation has been created.
These do carry some small upgrade issues since CSModules are only partially upgrade safe and Jobs are a gray area, but still acceptable. In either case the upgrade is pretty simple.
We do add some better extensibility around conversations in the next major version