If you mean, use a different Google account, with a different Google Voice number, for Line 2, then yes, you can do that. Just follow the same instructions you did for Line 1. Note that the OBiTALK web portal will allow you to select which Service Provider (SP1 -- SP4) to use as the default for outbound calls, and which of the two Phone line jacks will ring on inbound calls from those providers.
Also note: if connecting a two-line phone or two one-line phones, pay attention to wiring. The Phone 1 jack on the back of the OBi is a four-conductor, RJ-14 jack. The center two pins are Line 1, and the outer two pins are Line 2. This can be used with a four-conductor telephone cord to plug into a two-line phone's "L1+L2" jack. The Phone 2 jack is a two-conductor, RJ-11 jack. It's two center pins are connected only to Line 2. This is so that you could use the Phone 1 jack and the Phone 2 jacks, each with a two-conductor phone cord, to plug in two different one-line phones.