How to specify the source map for multiple files in command line?

Say I want to pack all css into 1 file, how should i specify the source map for bootstrap.css?

uglifycss --output css/app.min.css --max-line-len 800   ^
    jsplugin/bootstrap/css/bootstrap.css ^
    jsplugin/bootstrap/css/bootstrap-theme.css ^
    js/app.css


Thanks
