Hi yes it is possible as this is what I do now, I make the layouts in 04 then test and check them out in 06 for faults and to see if they run ok.
To do this you need to copy the map folder from Custom to your desk top and if you have done one the session which you will find in profiles.
You then open CMP in 06 and go to top left file click and select import content then browse to the desktop and the folders.
CMP will now extract the files and you can view them in the main list , you will then need to left click to highlight and then right click and select edit commit.
Now you can launch 06 and test out the layout.
PS you also need to make sure the content you used for the layout has also been put into 06.