waiting for input in command line after keymap

[JeromeSchmied]

I'm experimenting with keymaps for cargo commands, but I'm a bit stuck at cargo add <pkg>.
The problem is, I don't want to always type in the whole command: :sh cargo add <pkg>
but instead would like to use a keymap like: Space+l+a and then type the rest into the command-line of helix.

NOTE: I've made up a workaround: select the crate name (text), yank it to system-clipboard and use that text in shell for cargo add <system_clipboard>

keymaps:

[keys.normal."space".l]
c = ":sh cargo check"
t = ":sh cargo test"
r = ":sh cargo run"
# FIXME: how could wait_for_input be done?
# a = [":sh cargo add ", "wait_for_input"]
# workaround:
a = ["yank_to_clipboard", ":sh cargo add (wl-paste)"]
d = ["yank_to_clipboard", ":sh cargo rm (wl-paste)"]