You've got a few different options here. As you mentioned, Data Sources require some processing time and are often set up as a nightly feed, so I'll skip that one.
Regarding Demandbase - I'm not sure that I'm following. Are your customers logging into your Salesforce instance? You may alreayd know this, but Demandbase leverages an IP-based reverse lookup, so Demandbase would report on the company associated with the visitor to Salesforce.com. For example, if I have my own instance of Salesforce, with Demandbase reverse-lookup enabled on it, and my customer at Widgets R Us logs into my Salesforce instance from their office, then Demandbase would report on Widgets R Us. I hope that helps!