You can embed them in the torrent, same as the tracker. But the tracker has to handle all the state, while a bootstrap node just hooks you up with a few (or one) node in the DHT network. After that, it's fully decentralized.

There could other ways, embedding them on SRV DNS records, etc. It's the same issue as with getting a DNS server. You could in theory get addresses of bootstrap nodes from your ISP through DHCP (lol, sure).