EtchCo! You've Done it Again!

You can convert a typical bicycle into a stationary / exercise bike with one of these:

This has the benefit of making your typical bike more multi-purpose, since you don't need to buy a separate exercise bike for working out - great.

But you would need a dedicated spot for this - it's not a very portable setup - you probably wouldn't take it from room to room with you.

How about this? Hook the bike converter into a unicycle. It has a smaller footprint, and it a lot more portable. Granted, there would be no handlebars to slump over and lean on, but as a benefit, there would be no handlebars to slump over and lean on - you're working your core muscles to keep yourself upright.

It might be argued that a unicycle isn't very useful beyond the home workout, but aside from the fact that you might look silly using it in public (get over it - admit that you always look silly, stop fighting), the unicycle would be a lot easier to take on the bus with you, or even into your cubicle at work.

With speeds of 8-9 miles per hour, a unicycle is something you could use pretty much as a typical bike.