SQL Server TRUNCATE TABLE permissions
You could use this technique by Jonathan Kehayias to create a stored procedure that will allow the user to TRUNCATE a table.  

As Johathan says:


  "You can't grant truncate because for whatever reason, that permission
  doesn't exist.  What you can do is use a stored procedure and use
  EXECUTE AS OWNER to get around it."


Here is the sample code from the above post.

CREATE DATABASE foo
GO

CREATE LOGIN foobar
    WITH password = 'Pa$$w0rd';
GO

USE foo
GO

CREATE user foobar
FROM LOGIN foobar;
GO

CREATE TABLE test (rowid INT identity)
GO

INSERT INTO test DEFAULT
VALUES;
GO

SELECT *
FROM test
GO

CREATE PROCEDURE dbo.truncate_test
    WITH EXECUTE AS OWNER
AS
TRUNCATE TABLE test
GO

GRANT EXECUTE
    ON dbo.truncate_test
    TO foobar
GO

EXECUTE AS LOGIN = 'foobar'

EXECUTE dbo.truncate_test

REVERT
GO

SELECT *
FROM test
GO

USE master
GO

DROP DATABASE foo

DROP LOGIN foobar