Automator would be your best bet. Create a workflow that will get the specified Finder item(s) and attach them to a new email, then save it as a Finder plugin. Every time you want to send it, just right click the file(s), go to the Automator context menu and choose your action. You can have it send the email for you without having to even look at Mail.
If its the first time you've used Automator then it might take some trail and error to get it right but now would be a great time to start using it. I avoided it for quite some time thinking I had no use for it but now it does practically everything for me and I've only been using it for a week.