Can you replace the present perfect continuous with present continuous when a concrete time period is specified?

As I have learnt, present perfect continuous should be used when we want to describe some activity which lasted for concrete period of time and is not finished still.

For example, "I've been waiting for her for 2 hours already" or "How long have you been waiting for her?"

These constructions (especially the question form, where 'have' cannot be shortened) look and sound rather complicated. That's why I wonder whether it's acceptable to use present continuous (especially in speech).

Another logical argument to use present continuous in question form is the analogy with questions which doesn't touch time aspects like:

What are you waiting for?

Who are you waiting for?

Why are you waiting for her?

but

How long have you been waiting for her?

So, is it acceptable to ask

How long are you waiting for her?

One more thing: does present perfect continuous add some additional hidden value, like expectation for results or anything else?

You could say 'I'm waiting two hours', and no one would misunderstand you. I don't think there is any loss of meaning, but you might sound a little foreign. I think this usage is standard in some types of American-English. I could imagine a character on Seinfeld going 'Two hours I'm waiting - what is it with these people?’

In speech (but not in formal writing) you can say 'How long've you...'

Actually, there is a context where "I am waiting two hours" means something completely different (thanks Claudiu, Kosmonaut). If the issue was for example how long you were prepared to wait for a delayed flight, then you would say 'I'm waiting two hours (then I'm going home!)" to mean "I will wait two hours only"

So if the context is unclear, you need the 'have been waiting' construction.

No, the present continuous cannot be used in that way.

As the questioner notes, because the examples both refer to an activity which started at a particular point in the past, and is still ongoing (in this case, waiting), the (present) perfect continuous must be used.

Using the present continuous as shown in the final example would still be understood, but it sounds wrong.