I have not seen any 2FA options to include YUBI key. (I've got one of these too.) I am currently using 2FA via Google authenticator TOTP and it works very well. If you store your "secret key" in a secure place you can not only use your phone but the Google authenticator plugin in your browser. Here are the options and a link to the Account Security Page at RunBox.
Two-Factor Authentication
When Two-Factor Authentication (2FA) is enabled, you will have the following options:
Timed One-Time Passwords (TOTP): To use this option you will need a smartphone and some free software. This option works by giving you a login code which changes over time, in addition to your password.
One-Time Passwords (OTP): When you enable this option, the system will generate random passwords that you can use only once. Used passwords are discarded automatically can not be used again
.
Trust browser: This allows the server to trust your current web browser so that you don't have to use a 2FA code.
Unlock code: If for some reason you are unable to log in with 2FA after it has been enabled, this code can be used to disable 2FA.
https://help.runbox.com/account-security/
I think their 2FA implementation is rock solid.