vB variables in AdminCP data entry boxes

[Billspaintball]

Im having a little trouble here
I have a product with a data entry box in the AdminCP.
In that box I enter

Thanks $vbulletin->userinfo[username]
Test text blah, blah blah...

When the template is called the output from that is

 Thanks $vbulletin->userinfo[username]
Test text blah, blah blah...

But I need it to be

Thanks Username
Test text blah, blah blah...

so, what do I enter into the adminCP data entry box in place of $vbulletin->userinfo[username] that will result in the template outputting the correct username?