Postagging help needed

I want to disambiguate a group of tokens, starting either as
<Token postag="SENT_START¨/>
or as 
<Token postag="SENT_START¨/><token regexp="yes" postag="VGW" regexp="yes">en|of</token>

Can I do that having in only one rule?
I tried doing this having the second token as min="0" max="1", but that caused problems.

Any suggestions?