Stored Procedure Sebquery As A Paramater

Ok,

This sounds dangerous (and yes I know it is)
But its in a controlled enviroment and I really need to know how to do
this.

How can I pass a Subquery for an Exist or In clause as a paramater
Something like this

CREATE procedure dbo.mytry
@funk varchar(1000)
as

Select * from Customers where exists(
@funk
)

GO

So I would execute something like so

exec mytry @funk='Select ID From Customers where ID < 100'

Any Ideas, I have tried LOTS of things but I can actually get it to
work.

I need to use it conjunction with a 3rd party product that can only
select from a Stored Procedure, and I can only pass paramaters to the
SP.

Any suggestions ?

Thanks

Chris