I have not done that before, but I don't see why it wouldn't work.
Just be sure to adhere to the guidelines in the Release Notes:
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/crs/express_11_6/release/guide/uccx_b_release-notes-for-uccx-116/uccx_b_release-notes-for-uccx-116_chapter_01.html
For example, it says you cannot forward an Agent Extension to a Trigger. So, as long as the number you are forwarding, is not that, I think you'd fall within the supported configuration.
I have to admit, it does seem a bit low tech, and I might advise a more robust solution. But, it's your system, and you get to use it how you want to. Just be sure to forward on busy, unregistered, etc. to the Trigger, though the User can only set the CFA destination from the phone. Some phones allow forwarding of secondary lines, some don't.