5015 Radial to 40mm adapter with bullet

Many ducts using a standard 40mm axial fan include a center diffuser piece downstream of the fan hub. The idea is to improve the fluid dynamics of the duct/fan combination. However, when you replace the axial fan with some sort of fan adapter, you’re faced with a diffuser you don’t really want or need anymore. One solution is to cut it out, either by brute force or by using a CAD program to remove it.
This is the problem I faced when I found the dual 5015radial fan to 40mm design by bofus: