So, after talking it over more with the engineer we are going with a different option. The original option was a 4x12 glulam that spanned the full distance to sister to the original beam and support with 4x4 posts in the wall. The new plan is to use 12x30 C channel for the full distance, sister to the beam with through bolts, and support in the wall with 4x4 posts. The steel is going to be better at reducing the amount of sag and is significantly stronger according to the S.E. I'll post pics soon.