You need to do this if you haven't already (BB2OBJTYPES.RES will need to be present in your source folder)
I'm not so sure that a multiplexing routine would be a good fit for a flappy bird clone? Just hypothetically, you could do:
- Flappy Bird as a single 16px wide, 16 color sprite. Channels 1-2
- For an entire pipe section, including top, middle gap and bottom, do this as a single really tall, 16px wide 4 color sprite. That should allow you to get six pipes on screen at once.