Waterman carene rollerball and fountain pen compatibility

[Iphone]

I have a waterman carene rollerball pen.
I wonder if I can convert the Rollerball pen into a fountain pen.

Think about how I was the messages before the search and modification.

Are you sure that the Carene fountain pen cap fits the Carene roller ballpen cap?
Wouldn't it be compatible if I put the carne fountain pen cap in the rollerball pen barrel and put a very small cartridge about 3.7cm sold by Waterman into the rollerball barrel?