dict-xsyn converts word to synlist, what about backwards?

On my question about doing a first name search by it's synonyms, like

William Will Bill Billy
James Jim Jimmy

Oleg answered, that I can use dict_xsyn for that.

In the dict_xsyn manual, it is said that:
"This dictionary type replaces words with groups of their synonyms, and
so makes it
possible to search for a word using any of its synonyms"

This means, that if the dictionary sees the name "William", it will
replace it with "William Will Bill Billy", so that I can search with any
of them.

But what if the parser sees the word "Billy"? I want it to do absolutely
the same. If not, as far as I understand, I will make a default synonym
dictionary with pairs like:

will william
bill william
billy william etc.

Is there a way not to use this?