Has anyone successfully implemented this on a Draytek box? We have a 2930 and we have two broadband lines, with 2 defferent ISPs. We have failover working but would like to benefit from the increased bandwidth of bonding the two lines.

Any advice is appreciated

I think connection bonding requires ISP support because they'd need a similar setup on their end to bond the connections.
You can bond connections for VPNs though using VPN trunking, on the 2930.