Yes of course it is possible. Just write your own algorithm that can take multiple seeds run them through an algorithm then produce a seed to actually be use.
About polymorphism...
A polymorphic code is basically a code that can change itself or mutate itself but still accomplish the same thing. Basically it can patch itself, move parts of its code around, do things in different orders, rename things, etc.
A random number is necessary to decide in which way the algorithm should change itself. So a polymorphic code will use different types of seeds to help ensure its randomness.
Here are some links on polymorphism...
Polymorphic code - Wikipedia, the free encyclopedia
Polymorphism
Check those out they'll explain it better...