If you configure something in GW for authentication, it is valid for everyone. You can't configure a group1 to use pass+dynamicid and group2 to use cert+pass based on AD groups.
You select what type of auth to use (when you use SSL portal) or during the installation of a VPN client before even enter your username.
I think of something raw solution.
Let's say you configure 2 ways for authentication in CP GW settings:
1) username+pass+dynamicid
2)username+pass+cert
You can switch between them in the VPN client GUI or in the SSL Mobile portal.
If you find a way to install and configure the laptops for group1 to use pass+dynamicid, for group2 - pass+cert and lock this configuration in the VPN client GUI you will achieve what you're looking for. Of course this is a hard work if you have more of laptops.
Another really raw solution - if you have 2 separate GWs for VPN, on gw1 configure user+pass+dynamicid, on gw2 configure username+pass+cert. Group1 initiate VPN to gw1 and group2 to gw2.