'directory' like setting for artifacts?

Is there a setting to set what directory should be used when generating the url for each package in the packages.json from a satis.json that uses zip artifacts?

e.g. I have a satis config file like:

```
{
"name": "Intahwebz package repository",
"homepage": "http://satis.basereality.com/zipsOutput",
"repositories": [
{
"packagist": false
},
{
"type": "artifact",
"url": "zipsOutput/packages/"
}
],
"require-all": true
}
```

i.e. all the zip files are in the directory `zipsOutput/packages/` directory and I'm going to generate the satis files into the zipsOutput directory and serve that as the web root.

However after generating the satis files, all of the packages have a URL set to the full path in the packages.json like:

"url": "/documents/projects/github/Bastion/Bastion/zipsOutput/packages/zendframework_Component_ZendValidator_2.2.5.zip"

So in the web browser, the files have a url like:

`http://localhost:8000/documents/projects/github/Bastion/Bastion/zipsOutput/packages/zendframework_Component_ZendFilter_2.2.5.zip`

rather than :

`http://localhost:8000/packages/zendframework_Component_ZendFilter_2.2.5.zip`

I know there's a setting in 'archive' for when Satis is downloading packages itself, but this seems not to work when it's using artifacts that are already available.