The second iteration of 2v8 is now LIVE - find out more information here: https://forums.bhvr.com/dead-by-daylight/kb/articles/480-2v8-developer-update

Bots in Custom Matches

A special option to activate bots in custom matches allowing players to try out and practise a new killer before venturing out.

Otherwise, there is no way except having a public match. This is often depressing when learning a new killer. Since Dead by Daylight has added AIs they can be added to custom mode.