Combining two controllers as one

[Amadeus42]

I would like to know if there is anyway for Dolphin to use two controllers as one controller when configuring the game cube controller.

Details: So I've built an arcade cabinet for games I am emulating (various systems, including GameCube and Wii) for two players but due to the individual controller boards not having enough slots for all the buttons I want, I am stuck using a total of four controller boards, two for each player. Dolphin (and my computer in general) recognizes each of these 4 controller boards as a separate Generic USB Joystick. Is there anyway for dolphin to take input from two separate boards (for instance boards one and two) as one GameCube controller and do the same for boards three and four for GameCube controller two?

If there is any 3rd party software (that currently works with windows 10) I'm not against using it, but everything I've tried (including vJoy) has not been successful thus far (potentially due to my ignorance, but I can't find any way to enlighten myself in this manner if that is the case).

I've tried multiple methods as recommended by various google searches, but none have worked thus far.

[Billiard26]

Recent development versions allow you to choose "All Devices" in the controller mapping dialogs.

In Dolphin 5.0 you can right click the mapping buttons and manually choose different devices.