I still think that you're not losing anything by making the product itself (in some version) available through Kickstarter backers. Yes, kickstarter is taking 5%, but that's pretty reasonable when you consider what percentage is taken by drivethrurpgnow and physical stores. Yes, a large percentage of those people who pick those rewards may buy anyway, but why not give them another opportunity and time window to do so?
You could do:
$25 name an NPC
$X get a softcover printed version of all Y volumes in the adventure path.
$25+X name an NPC and get the softcovers
$100 name a statted NPC
$100+X name statted NPC and get the softcovers
etc.
That said, I realize there may be other factors in your case because it could impact your subscription model, maybe you don't ever want to do a printed version, etc.
Oh... or you could do some other bonus things... like a special map (physical or electronic) of the game's world/area only available through Kickstarter. Sure the adventures and sourcebooks may have a similar map, but maybe this is in a different style or is larger or is the only map that combines the whole setting in one place...
