Train maskrcnn OD and keypoints at the same time

Currently, I found it not possile train OD and keypoints at the same time on coco, since their dataload are separated,
so I think if it workable that, we directly using maskrcnn trained weights, load to a new model which add keypoint_roi_head to StandaredROIHeads
and frozen all weights except this keypoint_roi_head, then using normal keypoints dataloader to train.

My question is:

1). Is it possible?
2). How to frozen weights without changing d2 source code?