XPCE menu - fixed width

Question

This is my code:

listaw:- 

 new(SS, dialog('Rekordy w bazie wiedzy')), 
 send(SS, display, new(W3,text('Nazwy komponentów'))), 

new(M,menu(von,cycle)), 
 findall(B,failure(B,_,_),Y), 
 send_list(M, append, Y), 
 send(SS,open). 

I want to make a menu with fixed width. If I will write long text into menu, I want to have the same size of menu as before. Do somoene know how to do it? I can't find solution in XPCE manual unfortunately.