I've grown fatsia japonica and aucuba japonica in similar circumstances, and both look great with bamboo. Did well for me, provided with thick mulch and plenty of water while getting their roots down. I'd expect herbaceous anemones, such as honorine jobert, to do well too, as of course would ferns, assuming you avoid the moisture lovers. Both look best grown as large 'natural' drifts rather than just 3 or 4 plants in a blob. Shrubby euonymous (the evergreen variagated types) are also useful for tough spots and the yellow or white is handy for breaking up what can otherwise all get a bit heavy and dark.
Re. screening, a small climber in a nice square pot or large trough could be the go. I'd go for something like a large-flowered clem, so it isnt something that wants to be a beast and will suffer in a pot. Or, you could get one or two of the very ornamental ivies (clotted cream and buttercup are my faves). The benefits are tthat they'd thrive in very little soil, actively prefer dry shade, give you screening all year and need no support as they'll self-cling. Bung up a coupla wicker hanging baskets to put trailing begonias in for summer and pansies for winter (they both like it cool and shady but give loadsa colour) and your eyesore becomes a nice view. Oh, and if you're planting against the sheds, paint em dark brown - makes them recede behind greens of foliage and disappear. Thats what I think anyway! Bxx