Sorry to be the bearer of bad news but you do NOT get the "business select" fare when deviating on WN. All WN deadheads will be booked in "business select" and the company will pay the "select" price. If you deviate you only get the "regular" ticket price. This is a quote from the June 08 SIG letter.

Southwest Business Select: This was intended for scheduled deadheads on SWA as a way to alleviate some of the pain, especially on the mid-trip SDDHs that were prevalent at the time it was established. CTS should still book all scheduled SWA DHs with business select when available, however, the accepted fare (and your bank) will only reflect the cost of a basic ticket (w/o Business Select).

If you deviate on SWA, you can request Business Select, but the total cost of the ticket will be charged against your bank.