OnePlus devices generally receive a lot of support from the developer community and the OnePlus 5 is no different. Thanks to help from XDA Recognized Developer / Recognized Contributor nkk71, XDA Recognized Developer martinusbe was able to release the first build of MultiROM for the OnePlus 5. This comes with the modified recovery image, the MultiROM zip file, and an uninstaller just in case you want to revert these changes. You'll also find the APK for the MultiROM Manager application in our forum link below as well.

Check out MultiROM for the OnePlus 5

Thanks for the tip @Char_G!