As Nick said, if you do a right-click on the image in either the Library or Develop module and choose Edit In -> Photoshop Elements 10 it will export the image as a Tiff (or PSD file if you prefer, you can change it in preferences). It will open it in PSE10 and you can do what you want, save your work, and exit. When you go to save it should default the location to the same place as the original, but check anyway. When you're done, the new Tiff file should display in the Library next to the original RAW file (there's a preference option to automatically stack them as well - at least there is in LR5). You can now make further LR adjustments to the Tiff/PSD file, but they will be independent of the original RAW file. You cannot stack the PSE adjustments with the original LR adjustments to the RAW file - you have to create a new image file to manipulate (this is the same with regular Photoshop as well).