HTTPS shouldn't be an issue to fix, but OpenVPN gets the encryption mode defined at both ends, and both must match. Unlike HTTPS, you can't define several ciphers and just have the other end pick one.
However, in the settings there's this:
Renegotiate data channel key after n packets sent and received (disabled by default).
Renegotiate data channel key after n seconds (default=3600).
When using dual-factor authentication, note that this default value may cause the end user to be challenged to reauthorize once per hour.
Also, keep in mind that this option can be used on both the client and server, and whichever uses the lower value will be the one to trigger the renegotiation. A common mistake is to set --reneg-sec to a higher value on either the client or server, while the other side of the connection is still using the default value of 3600 seconds, meaning that the renegotiation will still occur once per 3600 seconds.
The solution is to increase --reneg-sec on both the client and server, or set it to 0 on one side of the connection (to disable), and to your chosen value on the other side.
I would advise that if people are unable to migrate from Blowfish in their OpenVPN configurations, they make use of these two settings to at least ensure the keys are re-negotiated in time. The default of 1 hour sounds safe unless you have very busy VPN links. --reneg-pkts would make doubly sure that the keys are negotiated often enough to make this attack nearly impossible unless the attackers were very lucky indeed.
New installations should probably look at other ciphers, I tend to stick to the AES ciphers. (See openvpn --show-ciphers for a list)