You can add custom toolbars to a different workbench with customize ( context menu of any toolbar ).
There you can add an icon form PART to PART DESIGN for instance. You have to check the usability yourself.
Just a note :
Some workbenches CAN interact, but we have seen trouble when this ist done extensively , which happens for instance when you use PART functions within a PART DESIGN Project and jump back and forth. We have for instance often seen users adding boolean operations from PART to PD Projects which further down the model created problems.