This is quite a special feature that SilverCart does not support out-of-the-box. But we could customize SilverCart for your client and develop this feature. Drop me an email to email@example.com with the detailed requirements if you are interested to obtain an offer for that.
Over the last weeks we had several bugs fix and now proudly present [url=http://code.silvercart.org/silvercart/overview]SilverCart 1.0[/url] final. The code is used by us in several live online shops. A short info on scalability: We will have an ecommerce project going live this month with 300 000+ products. The frontend still works smoothly. This is not only our merit, it also shows the capabilities of Sapphire.
As we continuously improve SilverCart with new features, enhancements and bug fixes we jumped to version 1.1 last week. Check out the [url=http://www.silvercart.org/blog/silvercart-has-jumped-to-version-1-1]change log[/url].
We already did some fixes and improvements so download the tip version from our [url=http://code.silvercart.org/silvercart/downloads]public repo[/url].