Compensatory picks are commonly used in dynasty leagues to reward or onboard new teams. While Sleeper doesn't automate this yet, you can manually add them to the draft board with a small workaround.
Start by adding extra rounds to your draft to account for wherever compensatory picks will be awarded.
For example, if you're running a 10-round draft with comp picks in rounds 4 and 5, set the draft to 6 or 7 rounds. You can do this by temporarily adding adjusting the number of supplemental draft rounds your league has in your league general settings.
When you reach the end of a round where a comp pick is being awarded:
Pause the draft
Head to the bottom of the draft board to assign the pick to the appropriate team
Once that's done, resume and continue as normal
After the draft wraps up, just make sure to adjust your roster settings back to their original configuration
We're looking into automating this down the road, but for now this is the most reliable way to handle it.