You could use a group 2 clematis that doesn't really need pruning, but you still need to prune the rose, so why not have two roses instead, one either side? As climbers, they'll both need pruning at the same time...

I have two roses either side and there are clems with them, one flowers late summer and both rose and clem get pruned in the spring. the other has a very early C alpine that gets pruned back after flowering when I do the rose. sometimes I have to sacrifice abit of the clems to get the best from the roses.

I would also go along the 2 rose route. The choice would be yours but go for ones that aren't too vigorous, perhaps about 8 foot. Easy to keep pruned and give a good air flow to help with molds and mildew.

I have a rose on each side, and a clematis on each side too, plus an evergreen winter flowering clematis! The Clematis I chose are both group 3 and I cut them hard back in late autumn at the same time that I tidy up the climbing roses. The evergreen clematis is left alone apart from tying in as it grows. I did have a honeysuckle, but it grew a bit too well.

I have metal framed arch with two climbing rose on one side and a honeysuckle (which is very vigorous) the other ,the honeysuckle trails right around and in between the roses ,and looks so nice throughout the summer.I have to carefully prune,especially the honeysuckle ,but its really worth it.