Creating a service that runs a user-installed package as root

[heat from fire]

Hi all,
 
First time posting on this forum.
 
I am trying to set up a service that runs "sudo mullvad-daemon" upon user 
login. The mullvad package is installed through Nix on a user profile.
 
I've tried creating a user service using Shepherd in a config file at 
"~/.config/shepherd/init.scm", but it doesn't seem possible to run the command 
as root.
Here's a snippet from the file:
 
(define mullvad
  (service '(mullvad)
    #:respawn? #t
    #:start (make-forkexec-constructor '("mullvad-daemon" "-v"))
    #:stop (make-kill-destructor)))
 
I read through here in hopes to find a solution, but to no avail:
https://www.gnu.org/software/shepherd/manual/shepherd.html#Services
Perhaps there is a service constructor with an option to run the command as 
root?
 
I know that I can define a Shepherd service in my system config file, which 
runs the command in it as root, but given that it depends on a user-installed 
Nix package, I'm not sure how I'll have to accommodate for that. The command is 
located at /home/user/.nix-profile/bin/mullvad-daemon.
I also tried creating a regular system service using service-type, but couldn't 
get it to work.
 
My only other alternative is to run sudo mullvad-daemon in ~/.profile and make 
an exception in the sudoers file to not require a password. This solution is 
messy so I wanna try to avoid it. I could also put the command in the Guix 
equivalent of "/etc/rc.local", but I don't think there is one in Guix.
 
Any ideas on how I can create a service that runs a command installed in a user 
profile as root? Or alternatively, a better way to run a command as root 
without password on user login, after sourcing ~/.profile?
 
Thanks!