Execute bash inside subshells

Say I have a command that puts me into a subshell (e.g. nix-shell). If I have a bash script that goes

enter-subshell
echo hi

the echo hi will wait to be executed until I exit the subshell. Is there any way to write a script that behaves the same as manually typing out both lines in order? In other words, subsequent commands get executed in the newly invoked shell? Edit: it seems what I'm looking to do doesn't have a general solution.