Manipulating Text,nText Data Types Filed In Tsql

I have to run a dynamic sql that i save in the database as a TEXT data type(due to a large size of the sql.) from a .NET app.  Now i have to run this sql from the stored proc that returns the results back to .net app. I am running this dynamic sql with sp_executesql like this..

EXEC sp_executesql @Statement,N'@param1 varchar(3),@param2 varchar(1)',@param1,@param2,
GO

As i can't declare text,ntext etc variables in T-Sql(stored proc), so i am using this method in pulling the text type field "Statement".

DECLARE @Statement varbinary(16)
SELECT @Statement = TEXTPTR(Statement)
FROM table1
READTEXT table1.statement @Statement 0 16566

So far so good, the issue is how to convert @Statment varbinary to nText to get it passed in sp_executesql.

Note:- i can't use Exec to run the dynamic sql becuase i need to pass the params from the .net app and Exec proc doesn't take param from the stored proc from where it is called.

I would appreciate if any body respond to this.