Tourists always seem to like the Greenwich foot tunnel so you could ride through Canary Wharf and then cross the river at the Greenwich foot tunnel, view the Cutty Sark and then start heading back into central London from that point? If you're lucky both lifts in the Greenwich foot tunnel may be working. At least the foot tunnel doesn't involve the faff of getting people to pay, unlike the cable car.
If you went as far west as Battersea Park you could then cross Albert Bridge and head north to go view Imperial, the National History Museum, Royal Albert Hall etc. and continue through Hyde Park.
I can provide a gpx track for the Sightseer if you don't already have the full route.