Answer
No — Aurena's External Navigation Link command mechanism is restricted to URLs prefixed with http:// or https:// specifically. Invoking a custom/local protocol handler registered on the user's own PC isn't supported through this standard command mechanism, and wasn't planned for near-term updates as of when this was raised. Achieving this specific requirement would need a genuine customization rather than a supported configuration option — check current release documentation for whether this has since changed.