Go into iTunes, and buy the apps you want through that. Once you've got them on your account as "purchased" (even if free) then you can download them to the iPad and it will only take the latest version your iPad iOS can use. Worth a shot and very handy for older iPhones that are no longer supporting the new iOS.
If old versions of an app are no longer on the app store you're stuffed.It's automatic. There is no option.