Using PL/pgSQL text argument in 'IN (INT,INT,...)' clause

Good morning,

I have a function argument blah of type text containing something like
     33,44,55,66
. Can I cast it in some way to use it in an IN clause as integers like
     UPDATE foo SET x = y WHERE id IN ( blah );
or need I revert to dynamic SQL (EXECUTE...) ?

Thanks, Axel
---
axel.rau@chaos1.de  PGP-Key:29E99DD6  +49 151 2300 9283  computing @  
chaos claudius