Ok... I feel you are confusing the English definition of "depend" with what it means in java when we talk about "dependencies". Let me try to explain this the best I can.
In java, when you say that Class A depends on Class B, you are creating the relationship where Class A is aware of the existence of Class B, and that it has access to Class B's compiled code. Class A depending on Class B does not guarantee Class A inherits from Class B or anything, but rather that Class A uses Class B for some reason (could be inheritance, or Class A might simply have a variable of type B ).
So you say that MyClass works without SomeInterface, which would mean MyClass makes no reference to anything SomeInterface related. Nothing wrong with that. Then you say you are adding some extra feature, which is coming from SomeInterface (am I correct?). When you add the extra feature to MyClass, MyClass becomes "dependent on" SomeInterface.
You may get this to work with reflection, but reflection should always be considered a last-resort option, since it is an inconsistent means of breaking normal java convention. There is absolutely no guarantee that reflected code will be portable, which oracle even warns about. For example, there are some security restrictions which may prevent reflection from even working. These security restrictions will result in client-dependent errors and crashes. The lack of stable portability (which is arguably the entire purpose of java) is the main reason reflection is discouraged.