Yes, I think it would be possible. Certainly a custom pen would be possible. But if you want to use a standard kit that you can purchase, you might have to modify some or all of the kit parts.
I suggest as a start, you do a google search for ballpoint pen refills. I think you will find some pictures comparing the available refills and stating their sizes.
Another thing you can do is go to a specialist pen shop and ask to see some Mont Blanc refills. Take along some Parker and Cross refills and do a comparison, as well as make some measurements. A metric ruler and a pair of calipers would be handy to take along with you.