- download the Fuse Fabric bundle (which is basically a FuseESB distribution with the pre-installed Fabric support)
- install Fuse Fabric on vanilla Karaf (or ServiceMix) container via OSGI feature
Although installing Fabric on the vanilla container is very temping, this option doesn't work well in the latest stable Karaf/ServiceMix/Fabric releases. Keep in mind however that, according to the information I've found on the mailing lists, the latest development versions of the Karaf/ServiceMix/Fabric work like a charm.
Since deploying snapshot versions of containers to the production is not an option, at this moment I would recommend to stick to the bundled version of the Fuse Fabric.
If you want to use this fine piece of software, you need to migrate your configuration to so called Fabric profiles anyway. With created profiles, migrating from vanilla ServiceMix to Fabric bundle is not a big deal.