unfortunately, unilateral leads are not really reported, especially not in Lead group. Sorry about that, we just never had a real project with them so there was no need to support them up until now.
I fear you need to write custom code for the group level stuff.
On single subjects, in the rare unilateral patients I visualized so far, I usually just place two leads in and ignore one of them (deselect in 3D viewer). But I fear – depending on what you aim to do in lead group, it won’t really work.