This is the million dollar question. I did tons of research on this (as you know, I'm selling a pair of RXL wheels) apparently the ones that come with new bikes are NOT convertible but the aftermarket ones as seen on bontragers website are made with dt swiss 240 hubs and are convertible and they include the conversion pieces when you purchase. The set that I have are already 15mm front and 142 rear and there are options to easily get qr on the front if someone really wants it but there doesn't appear to be an option to go to 135 on the back though I'm sure someone could fabricate something.
I found a guy on eBay who hand-machines billet alloy 15mm>9mm QR adapters. These simply slide straight into the 15mm front hub and is secured by two o-rings. This is about the best, precision axle reduction you can buy to date:
Zachariah, I still cant conceptualize how this can work in the rear. I took my set of bonty wheels and put them up to my frame and the front is obvious; the 15 thru ax hub is still spaced at 100mm so the adaptor slides through the hub and has the little nubs on the end to rest in the dropouts or you get a DT SWiss 9mm rws thru bolt and that will rest in the dropouts and clamp the wheel in. But I can't picture how the rear can work because the hubs are 142x12, not 135. Without being able to remove the endcaps, I must still be Shittouttaluck with the rear wheel.
I really love the look of these wheels, I'm wondering if I should see if I can find a hub with the same dimensions and just relace the wheel. I'd like to get a chinese carbon frame with the 142 rear end but it's just not in my budget right now