Have you tried the “Protype Titler”?
It’s abit convoluted, I admit, for what your doing.
But I believe you can achieve the result your looking for.
To get to it, open your Generated Media (text) and click the plug-in option.
Oddly enough, it seems an older version of Vegas had a plug-in (typing text) just for that…
or maybe I’m just imagining that. 0_o