Oracle Database Discussions

I have a Procedure called UpdateCase in an oracle database that I can not change. One of the parameters is an Object type. My goal is to call that stored procedure from MSSQL. We have created the linked server and a User Defined Table Type that mirrors the Object type in the oracle database. Here is the code to call the Procedure.

ALTER PROCEDURE [dbo].[spDMVUpdateCase]
    @CaseNumber INT = NULL,
    @User VARCHAR(50) = NULL
AS
DECLARE @ErrorMessage NVARCHAR(200)
DECLARE @ErrorSeverity INT
DECLARE @ErrorState INT
DECLARE @CaseRec AS CRASH.CaseSubType
BEGIN
    EXECUTE('Call UpdateCase(?,?,?,?)',
             @CaseRec,
             @User,
             @ErrorState,
             @ErrorMessage) AT ALIS
END

When I try to execute this code I get 'Must declare the scalar variable "@CaseRec".'
Is there any way to send a non-scalar variable to an oracle procedure from MSSQL?
Hope this is the right category to post in if not please point in the right direction.