I do have a plugin like that lying around somewhere (added a code editor keyboard shortcut to "toggle" the live_call line) but I proceeded to over-scope it by deciding that it'd be neat to allow inserting live_call line into every event at once. I'll get to this soon.
Viewing post in [Solved] Idea for GMLive integration or plugin
Snippet support was added since then and can be used to add an auto-completion item that inserts a live_call line / live_call_ext lines