We are using a "Flight Plan" process methodogy. It's a term that I have heard used by Ariba and by SAP and we have used it to build a supplier enablement process. Each "flight" is 2 weeks long. At the start of the first week is phone call communication to targeted vendors who completed an online survey about their capabilities. We also communicate internally who we are targeting for "take-off" in 2 weeks. That first week we run reports internally that detail a Vendor Reservation form( ie Master data that we want to be sure is clean before take-off). Than each day in the 2nd week we have 5-10 min calls with each vendor that is "at the gate". Ending in a Go/No-Go call on Friday for take-off on Monday. So far this has been effective at getting people motivated internally, with using terms that people can relate to. And the hand-holding approach with our vendors has led to supplier satisfaction and decreased the after take-off problems.
Focusing on suppliers that already transact in the ASN can make initial suppliers the "low hanging fruit". Have a team dedicated to working directly with suppliers who have little or no exposure to Ariba to ensure that they are getting their concerns with your company as well as with Ariba (such as technical questions) answered will go a long way.