I'd like to do the same, but the project is currently at design stage so I can't use the resourcing excuse.
How can I:
- Introduce the idea to the vendor (overcome resistance), and
- Structure the commercials (e.g. SOW for main vendor and T&M for the single contractor)?
I suppose another option is to introduce two competing Scrum teams, but we don't have much budget and I think handling the code merges could be difficult.