How do you get composer to install a non-composer package?

To include a non composer repository you need to set up a package repository. Which would give you something like:

{    "repositories": [        {            "type": "package",            "package": {                "name": "fguillot/picoFeed",                "version": "dev-master",                "source": {                    "url": "https://github.com/fguillot/picoFeed",                    "type": "git",                    "reference": "origin/master"                }            }        }    ],    "require": {        "fguillot/picoFeed": "dev-master"    }}

As an addition to the answer from @George, regarding the comment from @DavidOliver, here's how you should be able to change the package install target:

"repositories" : [    {        "type"    : "package",        "package" : {            "name"    : "vend0r/p4ckage",            "version" : "dev-master",            "type"    : "foo-library",            "dist"    : {                "url"  : "https://github.com/vend0r/p4ckage.git",                "type" : "vend0r/p4ckage"            },            "source"  : {                "url"       : "https://github.com/vend0r/p4ckage.git",                "type"      : "git",                "reference" : "origin/master"            }        }    }]..."extra" : {    "installer-paths" : {        "libraries/footype" : [            "type:foo-library"        ],    }}..."require" : {    "vend0r/p4ckage" : "dev-master"}