I have logged a specific feature request for this and referenced this thread in it. It should be possible to do this as a custom integration but it would require you to manually code it within the eCart checkout pages. If this is a route you would like to go you should start by obtaining the developer integration guide for ARB from Authorize.net. If you can get a sample script working you could go in and replace the values in it with eCart bindings for things like the item name, price and other cart details.