Hi Lukasz,
If I understand your question, you'd like to have the UX of the file dropper, but don't want it to upload it to a seperate entity? I don't see why, exactly, can you elaborate on that?
I think you either have to rebuild parts of the widget or develop a work-around, as this is currently not possible.
As work-around, you can move the file content from a helper object to the logo and delete the helper object after commit/save of the logo. Let's call the helper entity FileDropperImage and associate that with your Logo entity, grant the right permissions and link the Filedropper widget to that association. Then in the widget settings, go to Events > After commit microflow and create a microflow that looks like this:
Alternatively, you can trigger the logic shown above by some save button.
Good luck!