I'm not sure that you can just add the drivers to make it work. And even if you could I'm not sure that the XP Pro image would recognize them.
Which COA key did you use? XP Pro? Do you still have an XP_Tablet COA sticker on the bottom? If you had the XP tablet media you'd be further ahead. Just do what you did and use the SD method to install that instead.
You'll still need some of the Toshiba utility packages to make the buttons and rotation stuff work correctly but you should be able to get them off the recovery disc or off the website.
If you're game for a PXE boot to load the recovery image, that would be even better.