parsing variable name in a velocity template

Hi,

Is there a way to know the names of all templates variable (I.E: 
$variableName or ${variableName}  ) used in a template?  I want to create a 
HTML form that will let the user fill-in the velocity context but key names 
will vary  depending on the velocity template selected by the user.

The only way i'm thinking now, is using a Regex engine.