I'm physically handicapped so for me as a chemist I would happily supply spirodone over methadone since you get more doses per unit work.
Maybe a spirodone/loperamide analog since that is even less physical work to have to do.

Remember the amide doesn't necessarily mean it wouldn't pass the BBB since moramide is also an amide and strong analog of methadone.
I'm just exploring different ideas though, don't take it too religiously that I have actually attempted such work yet.
L-687,384 is not necessaily that easy to make though so if you had to go through all the steps it's for a superagonist not just skimping on the work load.