How to prohibit parallel scan through tableam?

Hi hackers,

I wonder how it is possible to prohibit parallel scan for the external 
storage accessed through tableam?
For example if I want to implement specialized tableam for fast access 
to temp tables, how can I inform optimizer that
parallel scan is not possible (because table data is local to the backend)?

Thanks in advance,

-- 
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company