Well... technically maybe, via patches. But the big question is, would it add value?
If I was Sony I would decide if there was any high profile, signature titles already out that would benefit, even partially, from the motion controls, and focus on those.
I suspect though (without thinking deeply I admit) that they'll find such titles thin on the ground.
All in all delivering the controls with say 5 stellar titles using them in different ways (or one key title like Wii Sports with multiple sub-games) would likely be a better approach.
You could have sports, of course, but also a Gladiator game with shield and sword (or mace, etc).
I think a lesson for Sony this gen was don't rely on 3rd parties to deliver what you need to make the HW shine. Nintendo always support their HW with strong titles, MS seems to be learning this lesson and I hope to see Sony do so.
They have a good 1st and tight 2nd party development infrastructure, but they need to use it more aggressively - the controls IMHO must launch with at least 3 good titles built from the ground up to support them.
And they should look at something 'flagship' for the controls, like a Wii Sports, or how 'Milo' is fast becoming the media flagship for Natal.
Try to be reasonable... its easier than you think...