prod-deployment.php

<?php

// ...

/* 
 * we resolve most options from the environment.
 * $resolvedOptions is a result of some computation earlier and contains most options
 * at this point in time
 */

$node = new \TYPO3\Surf\Domain\Model\Node($resolvedOptions['hostname']);
$node->setHostname($resolvedOptions['hostname'])
    ->setOption('username', $resolvedOptions['username'])
    ->setOption('password', $resolvedOptions['password'])
    // composerCommandPath is what you want, it's the absolute path on the target host,
    // or in this case prefixed with the correct interpreter
    ->setOption(
        'composerCommandPath',
        '/usr/local/bin/php7-70STABLE-CLI /kunden/***/***/***/***/composer.phar'
    );

// Use Application Type neos only, if you want your exported site
// to be imported on any deployment
$application = new \TYPO3\Surf\Application\TYPO3\Flow('host.project.de');
$application->setDeploymentPath($resolvedOptions['deployment_path'])
    ->setOption('repositoryUrl', $resolvedOptions['repository_url'])
    ->setOption('keepReleases', '5')
    ->setOption('sha1', $resolvedOptions['sha1'])
    ->addNode($node);

$workflow = new \TYPO3\Surf\Domain\Model\SimpleWorkflow();

$deployment->setWorkflow($workflow);
$deployment->addApplication($application);

Settings.yml

# Configuration/Production/Settings.yaml

# ...

TYPO3:
  Flow:
    core:
      phpBinaryPathAndFilename: '/usr/local/bin/php7-70STABLE-CLI'