String concatenation in Modify Headers middleware

Hoping someone might have some experience with the $tyk_meta and $tyk_context variables and concatenating them as part of a modify headers middleware. For example, if I wanted to concatenate $tyk_meta.hostname & $tyk_context.headers_Domain to create a string value of ., the dot . separator will be interpreted as part of the first $tyk_meta.hostname variable substitution and fail. Is there a way to escape special characters like the . or a way to quote out the tyk variables so then can be interpreted separate to the rest of the string.

Thanks Cam.