How to get Outlook to recognize a custom protocol URL in a plain text email?

[MBT]

Hi all,

I have a custom protocol that is registered in my users' registry and will
launch its associated program correctly from within an anchor tag in
Internet Explorer or from an HTML-formatted email. However, I have some
plain text emails coming in that will have these same custom protocol URLs
embedded as well. I would like Outlook to recognize these custom protocol
URLs even though they are in a plain-text message, the same way it does for
http:// strings.

If you highlight text in a new mail client and select Insert - Hyperlink,
the choices you get are:
file://
ftp://
gopher://
http://
https://
mailto://
usenet://
wais://

I hunted around in the registry for likely candidantes for where Outlook
pulls these values but didn't see any one definitive area (I think there are
actually probably two), and wasn't about to start hacking around (I know,
where's my sense of adventure).

Anyone know for sure of a place I can drop a value so that Outlook will
recognize my custom protocol and then start highlighting URLs with that
protocol in a plain text email?

Any help appreciated.

Thanks,
Marie

For the record, the protocol is notes://, to launch a Lotus Notes app in the
Notes client.