I suspect that it's not realistically possible to use this exploit against SSTP.
According to that answer, the attacker needs to be able to do two things in order to be able to exploit this vulnerability:
- inject data of their own before and after the secret value that he wants to obtain;
- inspect, intercept and modify the resulting bytes on the wire.
The reason that the answer says:
The main and about only plausible scenario where such conditions are
met is a Web context: the attacker runs a fake WiFi access point, and
The only way to do this in the context of SSTP would be to have some kind of compromised access to the windows machine that was trying to initiate the SSTP connection, and if you're in that situation you have far greater problems to worry about!
TL:DR The POODLE vulnerability needs some specific circumstances to be exploited, which are not provided by the standard use case of an SSTP VPN.