How in the world can you forget to install that upgrade

Anyway - here is a dirty little trick, that worked since Photoshop CS2: You can open 2 HDRIs at the same time, lay them out on your screen side by side, and then use the Clone Stamp from one to the other. Just sample with Alt in the left image, and paint in the right one. This is how I used to patch HDR panoramas together... It's not as flexible as rubbing through real layers, but with an undo here and there it can be a powerful workflow.
When the "Clone Source" image is just large color swatches, you can even paint pretty smoothly with the Clone Stamp tool....

I'm bummed out about the Basic/Extended split as well, the feature selection seems kind of random...
Blochi