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Bind brightness/volume and other special Fn keys in a tty

I am running Debian stretch on a Lenovo laptop with only a window manager (i.e.
no desktop). Out of the box, this configuration of Debian ignores the keys with
special Fn functions, such as volume up, mute microphone, brightness up, etc.

To solve the problem under X, I bound these special keys using `xbindkeys` (in
.xsession) to various scripts that perform the desired actions, e.g. invoke
amixer to up the volume on the master channel, etc. This setup appears to run
my scripts in sub-shells and so far has worked fine.

The problem arises when I try to accomplish the same effect in a tty running
Bash. So far I have tried binding the special the keys to script invocations
using `loadkeys` (in a `systemd` service).

Here is an example of what I submit to `loadkeys`:

    plain keycode 114 = F110
    string F110 = "my_volume_script_file_name some_parameters\n"
    
    plain keycode 115 = F120
    string F110 = "my_volume_script_file_name other_parameters\n"
    
    plain keycode 113 = F130
    string F110 = "my_volume_script_file_name yet_other_parameters\n"

When I press one of the mapped keys, this setup appears to submit my invocations
to stdin of whatever is running in the tty's foreground. If it is an interactive
shell, then everything works as expected (although seeing the command invocation
on the screen is annoying). If anything else is running in the foreground, then
of course the text submitted by the keystroke is not interpreted as a script
invocation, and the desired effect does not happen.

I am wondering whethere there is anything I can bind to my keys that would cause
Bash to interpret the text as a command to run in a sub-shell as opposed to
submitting it to the foreground process' stdin. Heck, if there were a way to
convince it to submit the text to a different file descriptor, I could probably
do something useful with that too.  

By the way, I looked at the Bash manual section on Readline, but found nothing
applicable there. 

My main goal, or course, is for special keys to work in a tty, regardless of
what is running in the foreground.  Are there other approaches anyone can think
of?

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This question is a slightly modified version of [Edward Ross' at Unix & Linux](https://unix.stackexchange.com/questions/704141/how-to-get-my-brightness-volume-and-other-special-keys-to-work-in-a-tty).