Typing national characters in a slightly different way

Typical way of typing national characters (if you need to use them) on a keyboard looks as follows:

This is an example for Polish ą character:

1. Push ALT.


2. Push a.


3. Release a.

As a result we 'll see ą on the screen.

Now, the question: I am looking for slightly more convenient solution:

1. Push and release ALT.


2. Push and release a.

As a result we 'll see ą on the screen as well.

I can easily configure emacs to behave like this. Do you know any hack/software or whatever which could allow me to use keyboard in all Mac applications?

Thanks!