How to assign string value to TEXT output parameter of a stored procedure?

Hello,

I am currently trying to assign some string to a TEXT output parameter
of a stored procedure.

The basic structure of the stored procedure looks like this:

-- 8< --
CREATE PROCEDURE owner.StoredProc
(
@.blob_data image,
@.clob_data text OUTPUT
)
AS
INSERT INTO Table (blob_data, clob_data) VALUES \
(@.blob_data, @.clob_data);
GO
-- 8< --

My previous attempts include using the convert function to convert a
string into a TEXT data type:
SET @.clob_data = CONVERT(text, 'This is a test');

Unfortunately, this leads to the following error: "Error 409: The
assignment operator operation cannot take a text data type as an argument."

Is there any alternative available to make an assignment to a TEXT
output parameter?

Regards,
ThiloIs there a reason you can't just do a select on it?