Yes, you can do that.
When you set up the two service providers, simply check-mark the appropriate boxes to select Anveo as your primary line for outbound calls, and for each of the two service providers to ring on Phone 1. This is all easily accomplished from the OBiTALK portal page.
When you occasionally want to call out using SP2, preface your call with **2. For example, to call 555-867-5309 using Google Voice, press **25558675309