The Lightroom double-exposure conundrum

I hinted in my initial Lightroom post that there was a situation where I still used ACR. It's when I need to do the double-exposure merge trick, simply because I don't know how to get this to work within Lightroom; perhaps one of my readers might be able to help out?

In the olden days, before Lightroom, you would open your raw file in ACR, create an exposure that made your ground look OK, but the sky washed out, hit Shift to have the "Open Image" button turn to "Open Object" to open the file as a Smart Object within Photoshop. Once there, you'd right-click the layer thumbnail and select "New Smart Object via copy", double-click the new layer thumbnail to open the new object in ACR, change the settings so that the sky looked OK, save and go back to Photoshop and mask out the ground from the top layer and, hey presto, you'll have a perfectly exposed sky to go with your perfectly exposed ground.

Now, with Lightroom this doesn't quite work. I expose the ground properly in Lightroom, export to Photoshop, select "New Smart Object via copy" and double-click the layer thumbnail... only to have a PSB file opened inside of Photoshop. No ACR action. For this to happen, I need to expose in Lightroom, write the image settings to an XMP sidecar (one keyboard shortcut) and then open the raw file from within Photoshop to force it to use ACR - where I then follow the above steps. It works but it's a bit backwards, it takes a few extra steps.

Anyone got any hints on how to improve this? Is there a way of getting this to work without having to take the extra steps? I imagine one way of at least making it ONE step shorter is to set ACR as the "Additional External Editor" in the Preferences dialogue to make sure it comes directly via ACR into Photoshop as a Smart Object, rather than having to convert it manually - but how do I do this? Ore are there any other suggestions?