You're not going to be able to increase endurance with a 1.25 mile bike ride.
HIIT/Tabata would have you pedal at 100% effort - an unsafe practice unless you are on an exercise bike or a closed track. Plus, as you already mentioned, you don't have shower facilities at work.
Instead, why not think of it as an emotional "workout." Go slower. Ride relaxed, use it to clear your mind. Focus on being a perfect bike-rider: calm, even breathing, smooth starts, smooth stops, safe swooping turns, aware of and focused on your surroundings. 10 minutes of rolling meditation to focus your mind could have real health benefits (and be a very safe way to ride.)
Then bust your ass on a much longer ride with elevation changes on the way home.