I had a similar problem - Halcyon BP with Hollis S38 wing. The BP has the top and lower/middle and no bottom slot, while the wing only has a top and bottom slot for the cam bands, not a middle/lower slot. So only the top slot lined up between the BP and wing. The BP and wing have the standard 11” spacing for holes and grommets.
That means I had these options:
1. Fit just the top camband through the wing and BP and let the lower cam band only attach to the wing through the slot. Given that many rec BCs only have one cam band anyway, I might have been fine with it. I would potentially use carriage bolts with large washers to help secure the wing to the BP through the grommets, especially that lower attachment that might flop a little
2. Use an STA, which is what I ended up doing.
3. Cut a lower pair of slots in the BP to fit cam band which I didn’t feel like doing. In your case you already have the lower slots.
In your case, an alternative to the STA might be to re-rig the BP/W DIR style as a single piece without the separate waistband. But that probably gets away a little from why you bought that style harness in the first place.
The other option for keeping the harness might be just to thread the top cam band through the BP and wing as normal. For the lower cam band, keep the waist band going through the lower slot, thread the cam band through the wing slot only and use a bolt to pass through the wing grommet, cam band, waist band, and into the BP to secure everything together.