I have seen very tiny router/bridges, clear down to an Ethernet dongle with a +5v USB power feed. Quite unobtrusive.

If possible: grab a router and install OpenWRT onto it, and turn it into a wireless bridge. Use the router to connect to the office WiFi, and have a wired connection to your laptop. Turn off the laptop’s wifi for good measure.

Alternatively, if work provides hard lines, bring your own router and turn off WiFi to provide a protected hardline.

There are many ways to prevent the computer from realizing what network you are on.