If you are looking to find somewhere for your B and C list scientists to go to work without dismissing them. I'd suggest an alternate take where you can assign excess scientists to work as assistants/co-workers/etc alongside the main scientist who is leading the research.
I'd suggest that the first assistant scientist only contributes a maximum of 10% bonus to the research (assuming they have a minimum of 10% or more bonus), the second contributes an extra 5%, and every other scientist after can only contribute an extra 1%.
So you have a Power and Propulsion researcher working on a PP project with a 40% bonus. You add the first assistant scientist with a PP bonus of 15% which is capped to 10%, a second assistant scientist with a bonus of 10% which is capped at 5%, you then add two more assistant scientists which get capped at 1% bonus each. So in the end you have 57% bonus to PP research.
I'd also make a condition a scientist can only assist with a project that they are specialised in. Or suffer a malus to their bonus if they are working on a project they are not speced into.
E: A bonus to this system would be that if the main scientist dies or retires then the system should automatically assign the most senior assistant to take over, would cut down on the micro a bit.