I would try wiring it like the existing diagram, but ignore the green and white wires from the bridge pickup (because you don't have them!)
I don't understand the workings of those Ibanez switches, but positions 4 and 5 are definitely going to work; I think positions 1 and 3 will work; I don't know what will happen in position 2 - either you'll get bridge humbucker plus neck split like you want, or maybe the bridge pickup will be grounded out and you'll just get the split neck pickup.