The page that I linked to, associating a device and the 90 days, has been around for a few years (at least 3), but from what some people have posted on here the association doesn't always kick in.
Are the apps that you might want to sync in the computer's iTunes library that you sync his iPad to, or have you got copies of them somewhere so that you can add them to it and then sync them instead of redownloading ? If they were bought on a different computer, and are still on that computer, then you should be able to copy them over to his iPad's computer - by default an iTunes library is stored under :
- Mac OS X: /Users/username/Music
- Windows XP: \Documents and Settings\username\My Documents\My Music\
- Windows Vista: \Users\username\Music\iTunes
- Windows 7 and Windows 8: \Users\username\My Music\iTunes
There should be a 'Mobile Applications' or similarly named directory under it - copy the apps to a flash drive, if not already done so then authorise your account on his iTunes (Store > Authorise This Computer menu option) and then add them via File > Add To Library menu option