I have EQ5. Never thought about doing your idea so I played around to see what I could come up with. The easiest way I can see is to go to your Worktable and choose Work on Block. Set up the block to whatever size is easiest to draw an octagon. Block size doesn't matter. Finish your design, making sure you add color to the slices of the octagon. Save the block.
Now go to Worktable and choose Work on Quilt. Go to Layout and change it to 1 block horizontal and 1 block vertical. Slide the size bar as far as it can go to the right. Mine would not go to 54". To get this size, you have to change your Preferences. Go to File, select Preferences. Click on Layout Limits. Under General, change Max size of block to 54". Click OK.
Now go back to Layout and you will be able to slide the size bar up to 54". On the right side tool bar, select Set Tool. Click your block and then click the center of your worktable to place the block. And you're done! Hope this helps! Have fun designing!