This ended up working for me:
"repositories": [
{
"type": "composer",
"url": "https://packages.zendframework.com/"
},
{
"type": "package",
"package": {
"name": "zendframework/zendsearch",
"version": "0.1",
"source": {
"url": "https://github.com/zendframework/ZendSearch.git",
"type": "git",
"reference": "master"
}
}
}
],
"autoload": {
"psr-0": {
"ZendSearch\\": "vendor/zendframework/zendsearch/library/"
}
}