Composer doesn't list forked versions of package

I'm trying to use the PHP BlockIO package -- https://github.com/BlockIo/block_io-php

It requires a forked version of the bitwasp/bitcoin library. When attempting to update it with composer, or install it, I get an error with a list of versions that generally aren't available in the fork:

Root composer.json requires bitwasp/bitcoin dev-minimal, found bitwasp/bitcoin[dev-master, 0.0.1, ..., 0.0.35.x-dev, v1.0.0, ..., 1.0.x-dev] but it does not match the constraint

I've checked to make sure that the fork has a branch named minimal, and that the name in the composer.json file on that branch matches, and now I'm lost. I only have the forked branch in this composer.json file, in order to isolate and test:

{
    "name": "shorton/temp",
    "type": "project",
    "authors": [
        {
            "name": "short one",
            "email": "root@host.local"
        }
    ],
    "repositories": [
        {
            "type": "git",
            "url": "https://github.com/doersf/bitcoin-php.git"
        }
    ],
    "require":{
        "bitwasp/bitcoin": "dev-minimal"
    }
}

Any clues on how to get this working?

We have a project that uses this library right now, and 'composer install works', but everything is locked at the exact current version because composer update will not work.