Is there a way I can make a set of passive pickups into active pickups?
No, you have to chage the pickups out.
You could add a preamp inside to guitar but they would still be passive pickups.
ummm there would still be passive but if your after a high out put (like in active PUs) try screwing your PUs up higher from the bracket. To do this you look at your guitar see the screws either side of the pickup tighten up to make the PU go up loosen them to make them go down