Bad news for you. It is not possible. I've been working in something very related to it a few weeks ago, as you can see here:
https://github.com/q2a/question2answer/pull/188
This is a first step towards that direction. It basically allows to change thousand and decimal separators by sending numbers through a function that the end user could override using a plugin. In that override any number can be changed into whatever character you want.
However, there are many numbers spread in the Q2A core code that don't need to be formatted (for point and decimal separators), so those ones won't be sent through the function not allowing them to be changed. That's quite a lot of work because it requires going through each line of the core and see if a number is output. If it is, it should go through the function I've added to that pull request. Once that is done then you can override the function with whatever you want.
And the worst thing, probably, is that the pull request is in the Q2A 1.8 queue... so don't expect this soon!
