Have you already tested an awesome brush by Pablo Dobarro?

The tool features a custom cloth solver than can be used within sculpt mode in real-time on localized areas of the mesh. You can control the cloth material by grabbing, dragging or pinching the surface. 

The brush is based on a simple physics solver that manages to give amazing results. It brings four deformation modes that control how the forces are created.

It also features an alternative plane falloff mode which drags cloth from an entire cross-section of the model at the same time. 

You can learn more and get the brush here.