Make a "xthread value" viewable for a Facebook sharing widget

[cakissimo]

Hello,

In my forum, forums who are interesting to share have a option "blank message" ON and all text viewable run with xthread, so facebook don't find any "meta-description" text to share.

Is it a way to put a specific (or several) xthread field value like a "post message default " to share it  ?  

Thank you