Hi Adam,
For me the problem is not only wanting the aerobars somewhat higher, but also a fair bit closer than the steer.
I'm using Syntace C2s so there's no option for fore/aft correction. Hence a set of risers wouldn't help me out.
You wrote that you used to work with a double stem setup. Was this on the same bike as in the picture? It's hard to see in the picture, but it seems like there is not much room left for a second stem?
On my bike, there is 68mm of steerer tube sticking out. The headset is already quite low, so not much to gain there. So unless someone can point me towards some ultra-low stack (<35mm) stems, a double stem setup seems not possible for me.