Disclaimer on demand / shared stationery?

I have a group of users that need to add a disclaimer to at the bottom of an email on demand. Not all emails they send out would get this disclaimer, it fact they may send to a user one time and it would not be sent the next time they sent to that same email address.

How can this be done?

The one big constraint I have is I CANNOT modify the mail template design in any way.

One thought I had was to use stationery. I created a DB that distributes stationery. It does this by sending out an email with a button. The button adds or updates the stationery in the users mail db from a central location.

What the potential owners of this DB do not like, is the fact that the user’s need to press the button to have the disclaimer updated. They wanted to happen automaticlly.

Any idea on how this can be done?

Without modifying their mailin DB, I do not see how it can be done.