Take 1/2 of the bauble, cover part of it up with clay and mold the top dome part of it, captain america costumes basically to where you want the eyes diameter to be. Pour in some silicone, let it cure and cast a dome piece. I recommend doing some test pieces to see exactly how much resin is needed to have 2 proper sized eyes (my white ones were way too small, and I had detailed them before realising it).