Simulation of report parameters in T-SQL

Hi! I hope this is not a stupid question ...

I'd like to "simulate" multivalue report parameters in t-sql. Background is, that I'm developing statements for report datasets with management studio for convinience. The statements need to apply a filter based on a report parameter like this:

select a, b, c

from datasource

where a in (@listofitems)

Which works great in reporting services, since @listofitems is converted to 'item1', 'item2', ... by reporting services. I tried to simulate the parameter by using:

Cheers,

Martin.