Yes lots of ideas of things to prevent him as PM.
Spend 5 minutes a day doing something - anything. Even if it's on social media call out spin and. rhetoric that are factually inaccurate.
•If you are in Johnson's constituency vote tactically so he loses his seat.
• if you are in another constituency vote tactically for whoever can beat the Tory unless you have a really nice moderate one (and many of those have been kicked out anyway).
• put party loyalty to one side if you have an extreme candidate.It's only for 5 years and you can go back to party loyalty once the party has been cleaned up.
• Become politically active - join a party closest to your beliefs and help clean it up.
• Join a local protest group.
• Recruit one friend to become more active pointing out Johnson's failings.
• Sign petitions or protest against underfunding of health or education, sign petitions or protest against power grabs by the executive,
• Spend your 5 minutes a day commenting or contributing to organisations like InFacts that try to fact check politicians spin.
• Comment against extremists on newspaper comment sections, social media, number 10 website etc.
• Write to your MP , write to thank other good MPs.
• Help crowdfund organisations that try to combat extremism or deceits.
Every little helps.