Agree with what FDXLAG posted, and #1 (b) is what you might be thinking of.

Back-end DHs (where you pretty much by definition are AT the scheduled start of the DH) are a free-for-all: go wherever you want. That's a straight-up deviation. Or in FDXLAG terms, going from XXX (duty location) to YYY (anywhere you want).

The problem is 1(a) and 1(b) combined for you. In order for it to count as a deviation you need to end up in the scheduled city for the start of your trip (in this case Memfo since you are sitting reserve). So - start where you live, but end up in Memphis and you will be OK (but will, if you are a Boy Scout, declare the ticket as taxable income under the new rules).

You might be able to look at the Hotel-in-lieu-of-DH rules, but I think they only allow a 24-hour layover domestically.

If you want to go on vacation and have bank $$$ available, just jumpseat to where you want to be and then buy a ticket to Memphis.