Custom constants for Communications Messages

Hey Guys,

I have a generated key that I'm using to authenticate users (a hash link described here: https://premium.wpmudev.org/forums/topic/membership-how-can-i-offer-a-direct-link-url-so-no-login-is-required ).

I'd like to include this in an email to new users through the Communications tool in Membership. Is there a filter to add custom constants like %username% or %levelname%? I'd like to do something like:

Hi %firstname%,

Your URL is: %generatedlink%

Thanks guys!

Joe