Welcome to the forums, ipfnd

Of course there's a way!

In general, you would create a Zone and then use that Zone to define a trusted Network. This would allow unimpeded traffic to/from the printer.
However, in your scenario, this would mean the other folks would have access to your computer.
So, let's take this approach.
Go to Security/Logs. Right-click and select "Clear all logs." Then have someone try to access the printer (with firewall fully enabled). It will of course fail. Immediately go back to Activity/Logs. Right-click, select "Export to HTML." Save the file, and reopen it. Highlight the entries there, and Copy them. Then Paste those into your next post here. You can edit your personal/external IP address if it shows up, for privacy (you need not worry about an internal/network IP).
This way we'll see specifics as far as port, etc, which should help us create some more tailored, secure rules.
LM