Yes, as long as you have both ACBC and CBC licenses, you can insert both multiple ACBC exercises and CBC exercises within the same SSI Web project.
To make an ACBC exercise that just has a BYO question, just specify that there are to be no Screener pages, no Must Haves, no Unacceptables, and no concepts brought forward into the Tournament. Program the ACBC exercise otherwise as you normally would.
Then, add a CBC exercise directly after the ACBC exercise.
For users without an ACBC license who want to add a BYO question prior to the CBC exercise to introduce respondents to the attribute and levels, they can add a series of drop-down Select questions on the same page prior to CBC (or with more sophistication can add a Free Format question with a BYO question).