Currently, the only solution I can think of is to set the Project option to "package", which enables the CTRL + SHIFT + L shortkey to execute devtools::load_all(".").
Then in .Rprofile I change the functionality of devtools::load_all("."):
rlang::env_binding_unlock(env = asNamespace('devtools'))
assign('load_all', function(x) source('some_script.r'), envir = asNamespace('devtools'))
rlang::env_binding_lock(env = asNamespace('devtools'))
Now when I press CTRL + SHIFT + L, some_script.r gets sourced.