[Brian]

OmniFocus includes a Clipping service which does something along these lines - if you haven't already tried that, it may save you some work. It can be configured to add the clipped info to the Quick Entry window, and can also add a link back to the message in Mail.

The "Clipping material from other applications" page in the Help menu material is a good starting point on the feature - let us know if you have any other questions - happy to help!