Parsing Varbinary Data In T-SQL

Hi,

We serialize a custom object into a byte array (byte[1000]) and store it in a SQL Server 2005 table column as varbinary(1000).
There are a lot of rows retrieved with each SqlDataReader from C# code: up to 3,456,000 rows at a time (that is, roughly 3.5 million rows).

I am trying to figure out what will be more efficent in terms of CPU usage and processing time.
We have come up with quite a few approaches to solve this problem.

In order to try a few of them, I have to know how I can extract certain "pieces" of data from a varbinary value using T-SQL.

For example, out of those 1000 bytes, at any given moment we need only the first 250 bytes and the third 250 bytes.
Total: 1000 -> [250-select][250-no-need][250-select][250-no-need]

One approach would be to get everything and parse it in C#: get the 1st and the 3rd chunks of data and discard the unneeded 2nd and 4th.
This is WAY TOO BAD.

Another approach would be to delegate the "filtering" job to SQL Server so that SqlDataReader gets only what it needs.

I am going to try a SQL-CLR stored procedure, but when I compared performance of T-SQL vs. SQL-CLR stored procs a few weeks ago, I saw that the same job is done by T-SQL a bit faster AND (more importantly for us) with less CPU consumption than SQL-CLR.

So, my question is:
how do I select certain "pieces" of varbinary column data using T-SQL?..

In other words, instead of
SELECT MyVarbinary1000 FROM MyTable
how do I do this:
SELECT <first 250 from MyVarbinary1000>, <third 250 from MyVarbinary1000> FROM MyTable
?

Thank you.