You would do something like
--8<---------------cut here---------------start------------->8---
(connection-local-set-profile-variables 'remote-direct-async
'((tramp-direct-async-process . t)))
(connection-local-set-profiles
'(:application tramp :machine "randomhost") 'remote-direct-async)
--8<---------------cut here---------------end--------------->8---
`remote-direct-async' is a profile name you could choose
yourself. `tramp-direct-async-process' would be the respective Tramp
variable.
That looks very reasonable. One bonus is that the machine is specified
by the hostname only.
Which would avoid the difficulty of tweaking the regexp (e.g. I had a
problem - on a different machine - that my url included a port, and
that needed to be reflected in the regexp as well).