I've read many recent (in the last couple months) reports of people using their recently purchased WDW tickets at DLR.
You have to do it day by day though, turning a day from the WDW ticket into a day's DLR ticket. I believe it's done at the gate, but I could be wrong. HOpefully one of the many who has done it recently will pop in and tell you if it's changed at the gate, ticket counter, or guest services!
As long as it has the non expiration option, you CAN use Magic Your Way tickets at DL.
Yes, it has to be done each day, so you can't get a 2 day hopper for your 2 left over WDW days. But you can go 1 day, get a 1 day hopper, then another day and get another 1 day hopper.
It can be done at the turnstyle, ticket booth or Guest Services.