[Evolution] How to reference substitutions in a template?

[Jo-Erlend Schinstad <joerlend schinstad gmail com>]

I'm exploring the Template plugin for Evolution, which seems really
useful. But how do I
reference my constants (defined in the plugin config) in the template?
For instance,
I have a constant my.name, which I'd like to reference in the mail like:

"Hello, my name is $my.name, and blablabla.

Best regards,

$my.name"