You can do it that way Ed but them your faceplate cant be used for anything else if you look at my last pic you will see that I have created a spigot on the back to fit my chuck also what if you need more than one disk then you will need another faceplate I will make up more disk for different grits and for sanding wood
Like Woody says Ed a spigot is a great way to go as it leaves your faceplate free for other work.
If you have spare faceplate's or don't see the need to use it for anything then why not try it out
These are faceplate mounted although the pictures with my boat on don't show it have a look further down the page to see Terry's.
http://www.penturners.co.uk/your-tips-jigs/922-budget-lathe-sanding-jig.html