Sip trunk grouping

Hi,

I was wondering if there is an easy way to group two or more sip trunks. I manage to make this work on zap channels and it works great. It automatically checks the zap trunk that is not congested and use at to go out. The bottom line is that you can actually use the zap channel simultaneously not just a failover specifying which channels goes first and next which is pretty neat. What is the easiest way to do this on SIP trunk?

SIP trunks can use all the bandwidth available, so it would only make sense to load share if there was some funny commercial constraint.