[atlas] Traceroute with GRE protocol possible?

Hi, I'm working for a company that gives customers access to PPTP and L2TP tunnels. Some of our customers have internet access via tv cable - without an exclusive public IPv4 address. These customers are more and more having trouble connecting to our systems via PPTP and we can't see any packets on our tunnel routers coming from these customers. A normal traceroute does not show anything weird and goes through to our servers... But with a traceroute --protocol=47 we would be able to find out which system is blocking the GRE packets used by PPTP. Is there any possibility to make GRE traceroutes with the ATLAS probes? Thank you! Greetings from Wuppertal, Germany Max