Normally, you'd be asking someone to record a challenge and post it to Cajole, and backers of your campaign would be paying to see it before anyone else.
But sometimes, in unique situations, you might want to Cajole someone to do something specific where this isn't possible. For example, cajoling them to do something on their established live-stream, or to post a ridiculous meme on their social media channels.
So how would your Cajole's video proof give your backers the advance access they are buying when they back your Cajole?
Let's go with one of the above examples, specifically the established live-streaming one.
Imagine your Cajole is:
NINJA: We will pay you $25,000 to do a 24 hour live-stream in a speedo
In this scenario, backers would need to be explicitly informed that the advance access they are accustomed to will not be to the live-stream in this case.
In your Story section of your campaign, you would need to disclaim that:
"Due to the nature of this Cajole, the video proof you are buying access to is not video of the live performance, but of [insert what the video proof would show]."
This way, informed backers can still decide to join a Cajole campaign without being surprised later that the general public might have access to the Cajole at the same time they do.
When describing what is required by the video proof during your campaign creation, in this case you could require that Ninja record a video announcement thanking your backers and announcing to them exclusively when he will be completing the Cajole.
You should require that the information in the video proof he's submitting be kept between Ninja, you as the creator, and the backers exclusively. Ninja shouldn't share this on any other forum, or promote it elsewhere. The backers are the ones who have paid and deserve access to this information.