How to add a line in the middle of the file (not at the end)?

I've been struggling to add lines within a file using s3e.

Example doing this with sed:

$ seq 3 | sed '2i hello'
1
hello
2
3

There is a way to do this in s3e?

I’ve found that s3e has an option called 1. Add lines, but it only allows adding lines at the end of the file.

PD: I've been testing some POSIX shell scripts to use with adb shell, to edit some markdown files in Android devices. I found out:

• shfm: A nice minimal file manager.
• shedit: A nano-like text editor.
• mel: An ed-like line text editor.

There are some sh text editors that didn't work with adb shell (but do work inside dash), like: alte, poshed.