As mentioned in the previous answers, you can say "I like you twice/thrice/X times as much (as someone/something else)."
I would definitely add to that:
"I love you to the nth power!"
"I love you exponentially/factorially as much"
The following is also possible, but I think that most people would object, unless they have a CS/math background.
"My love for you is O(n^2)" (or more generally O(f(n)), for any f(n) you want to choose)