Hi!!
I was doing some digging about k9 Advantix and stumbled upon this forum:
http://forums.anandtech.com/showthread.php?t=317426
The third poster down mentioned something about for her dogs, she uses frontline and she buys the 3-pack meant for bigger dogs and measures out the appropriate ml for her smaller dogs and it ends up being more like a 6-pack...for the price of a 3-pack!!
I think this might be an okay idea but I would like to check with the other members to see if they have ever done this method and would recommend it.