Move launcher to another app

I'm using FirefoxPortable from this website as my daily browser for over 10 years now.
I keep it on a truecrypt (veracrypt) container, and have it registered as default app. To launch the browser, you have to mount the veracrypt volume with a password first. I secure my history and passwords this way (as well as other sensitive apps, such as messengers and email clients).
I dont't install programs at all, I don't like to clutter Windows, and Windows does a poor job on keeping your data secure especially if the pc is stolen, so please skip the argument from "you should have a proper install, not a portable app" domain.

Problems started with Windows 10. For some reason, as the truecrypt volume is not mounted on system boot, RunTime Broker goes around and wipes HTTP/HTTP setting for the default app, because the path to the .exe is invalid (as the drive is not yet mounted on boot). You you have Edge, it resets the setting to this browser, and uses it to open urls from apps. So I have to re-register Portable Firefox as default app after each truecrypt mount, which is tedious.
To avoid this from happening, the exe must be present on a drive mounted on boot.

Having a .bat doesn't work for file associations, and converting them to .exe is a crippled solution.

I want to have FirefoxPortable.exe launcher on say drive C:, while keeping the rest of the app in another location.
I suspect I could do it by placing the bundled launcher and creating some sort of .ini nearby (I wish to avoid command line arguments as they are hard to pass in windows registry where default programs are set up).

Could I do it with the bundled FireFox launcher?
Should I use the vanilla launcher and create the .ini pointing to the desired app location myself?

Thanks.