I don't know what the plan looks like but there's no problem using a swept spar. You just need to use the right sort of joiners. In my sketch here the spars are joined at the center with a flat delta shaped top and bottom joiner. Then standard webbing is used to box the whole works in. This is actually the proper way to do a spar join in that it joins the spar caps togehter with more material out at the surface rather than a relatively whimpy piece of plywood. where only the outer edges of the plywood are doing much.

There'll be some sanding of the points on the delta joiners needed to allow for the spars being tapered towards the tips but it's minor.