I'm supposed to be able to Cast two conjured swords at the same time, and I have seen it work before, but I can't seem to do it lately.
You'll want to left-click and hold, then right-click and hold. You'll see both hands doing the separate casting animations (even if you have the dual casting perk for conjuration). Release both and viola, two conjured swords.
Dual casting seems to do well with summoning, due to the duration boost. Strangely, I dual casted an alteration spell which is supposed to make it stronger, but got a longer duration instead.