I am in the wrong zone for you, but Peter Schneider's book (he gardens in Ohio) "Right Rose, Right Place" is a good place to start. I think any flexible cold hardy climber would work - you could train it over the wall just as you would along a fence. Schneider recommends Phyllis Bide as being ever blooming and very cold hardy. I grow it up a tree - here's a picture. It has thin flexible canes.

Jackie

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Check out John Davis. Winter hardy with no protection in my z4a area, heavy spring bloom flush with lighter repeats thru out the summer & fall. Will grow as a small climber (about 8') if you give it support but if no suppport will arch over at about 5'

Here is a link that might be useful: John Davis

How much fragrance does John Davis have?

Also, how thorny is it?

Fragrance is very light too my nose & not very many thorns.

not repeating but not prickly either, and with the most remarkable pure myrrh scent, Ayreshire splendens is the complete draping ground eater. A totally gorgeous, healthy and hardy field rose.