Hi Alexander,
SVG++ doesn't support SVG 2.0 Draft features. But anyway at first glance on SVG Parameters I would say that they should be implemented on other layer than SVG++.
If you are using XML DOM parser and don't need topmost performance it can be done by modifying DOM in place with parameters values before processing it with SVG++.
I can provide you with further suggestions if you really need this feature in SVG++.
Regards,
Oleg