how to override reflection getproperties

I would like to override reflection getproperties() function to return certain property only. For a simple example:

class A{public int a1;public int a2;}

If i make this call:

typeof(A).getproperties() 

I would expect it to return a1 or a2 depending on logic determined at run time. I tried to override the function in my class but it always error out saying there's no function to override with.