I'll try and see if I can come up with anything coherent.
An INFP may do this, but:-
Actions are usually far to indirect to express feelings. One could be helping someone because they like helping people, because they wished they liked helping people, to fit and and be thought well of, etcetera.
Through an action alone there is no clear way of deciphering the feelings behind it. Whether your own or another's.
Same goes for Fi. Fi could be seen as a series of values, or the things behind those values. The reasons for helping are just as varied in this case. They may value helping directly, they may value the productivity of society they think is brought about through helping, they may simply value you their own fuzzy warm feeling when they do help etcetera.
So I doubt INFP's would find much satisfaction in expressing through those means, because of how futile it is. The satisfaction from doing this instead will come straight from Fi and feelings that go along with it. The fact that they are moving closer to their own image of perfection or something along those lines.
Through emotional gestures (hugs)?
See above.
Through writing them down or other creative proccesses?
Well, one way of expressing it all can be to make another person feel it all (even that probably wouldn't express it perfectly, or at least probably wouldn't satisfy the desire INFPs seek to fill through such expression). Due to the quite strong ineffability of both Fi and feelings, that is a very difficult task.
It could bring satisfaction and I could certainly see INFPs attempting to do it. However, I think INFPs like to do those processes based around Fi, not because others will understand them through seeing the results (unlikely), but because it helps them understand it themselves. Clarifying the goal and starting point of life, so to speak. It also can bring about an idea that something non-human would understand (e.g. god), that they have left a path to understanding their Fi if anyone is ever capable of doing so, or simply direct glee from expressing it through their own internal code (my experience).
Or do you prefer not to express them at all?
This is a successful route, I find.
Simply describing, through straightforward words, the inner workings works well too. Though faces similar troubles to the other methods. Alas it can be important to a lot of INFPs to express Fi somehow, and each will likely find a unique and equally flawed way of doing so.
It's important to remember in all of this, how difficult it is for an INFP to understand their own Fi. Similar, I imagine, to an INTP trying to understand their own Ti. It makes it even messier when you look at Fi through the lens of Fi, as it will assume certain things to be universally true and not realise that it is actually only true for Fi.
