我可以使用MEF控制对象创建吗？

I need to add some extension points to our existing code, and I've been looking at MEF as a possible solution. We have an IRandomNumberGenerator interface, with a default implementation (ConcreteRNG) that we would like to be swappable. This sounds like an ideal scenario for MEF, but I've been having problems with the way we instantiate the random number generators. Our current code looks like:I need to add some extension points to our exis