It's a shame. My office router does:
- IPSEC
- L2TP
- PPTP
- GRE

My N900
- openvpn
- vpnc(Special Cisco Client)

So anyone willing to invent another VPN-Solution

Yes: pptp would be a nice solution. It's not that secure
but it's easy to handle as most routers have at least
pptp passthrough.