When you want to bootstrap from a sample which is not included into a standard bundle, do the following:
Init from empty
jam init empty
Now install the mix with needed .sample:
npm install <mix npm module>
Note, that installed mix have to include the sample you want named by sample convention (e.g. platformer.sample)
Now run:
jam bootstrap platformer
Collider.JAM will scan included mixes for available sample and will mix in needed sample when found.