Hi Mazzerati, first of all welcome to GoY.

Post your thanks in the comments box under the answers to your original question, that way those who answered your question will be notified and see your thanks.

Posting it as a separate question, Moongrower may not know what question you are thanking her for.

Some of the smaller clematis will grow in pots. is it possible to uncover a small patch of earth anywhere? In an area the size of a paving slab you could plant a hydrangea petiolaris which would easily cover your wall in time, but its too vigorous for a pot. Alternatively you might consider softening the look of the wall with something like pots of bamboo. Or you could fix troughs near the top of the wall and grow things to trail down. Or wall troughs at various heights - many options for planting. (Don't make the mistake of getting ones that are too small though - larger ones are better for the plants and don't dry out so quickly as small ones) Makes a difference which direction your wall faces. as to what will do well.