Is it possible to Create a FW Alias from the contents of a local file

[IsaacFL]

On my opnsense, I can see that the contents of the file /tmp/igb0_pdinfo contains the ipv6 prefix that is delegated via DHCPv6 on the WAN interface.

I would like to create a FW Alias for the ipv6 prefix (for me a /56) but can't figure out how to do it.

I tried an Alias of URL Table (IPs) pointing to file:///tmp/igb0_pdinfo as the URL but that didn't work.

I see in the General Log:
error fetching alias url file:///tmp/igb0_pdinfo

I also tried file://localhost/tmp/igb0_pdinfo with the same result.

Is this possible to do?