Ciao,
it's more easy than you think. Until this morning I never did it (i'am on Mac only since 2 months), but I wanted install the new beta of Safari 3 so I gave a look around and discovered that it is the dist file inside the package witch has the version info inside.
Download the driver, copy to desktop, open the package then open the dist file (copy also to desktop and open with textedit), in this case it's aplekeyboardsoftware.dist, scroll down until you see this lines
if (!plist || system.compareVersions(plist.ProductVersion, "10.4.10") < 0) {
my.result.message = system.localizedStringWithFormat('systemTooOld');
my.result.type = 'Fatal';
return false;
change the product version to the one you desire, save, put the dist file back to the package an install....
I did it with safari 3 beta 3 and Quicktime 7.02 and works perfect. I was able to install also the keyboard driver, but i don’t have one so i don’t know how it works. The install anyway worked.
Don’t forget to repair permission
Ciao