is it possible to specify _natively_ (in the BaselineOf spec itself) a conditional loading of packages?

Example usage:

I have package with extensions for Calypso, but Calypso is not always loaded, so I want to load the package only if Calypso is present.

The ugly way (because it's a hack and you cannot see the condition by looking at the project spec):

The imagined way (or something along the lines):

spec package: 'My-Calypso-Extensions' with: [ spec condition: [��self environment includesKey: #ClyBrowser ] ]

Is this possible? Or is there some other recommended way how to approach this?

Thanks,

Peter