The faster route is for each "drone operator" candidate to pursue their own certification and pilot's license under FAA Rule 14 CFR Part 107. This involves a knowledge exam covering everything from flight operations, applicable regulations, emergency procedures, radio communications, and the like. There are numerous "ground schools" in the private sector that offer preparatory classes.
The third—and most complete—avenue to get well-trained UAV pilots into the agency's ranks is to pursue both paths in parallel, with the PD obtaining a COA and each pilot getting their Part 107 cert. Once the COA has been issued and the pilots have their Part 107 cert, it's strongly recommended that regular training operations continue, ensuring proper adherence to the COA and renewal of those Part 107s.
Taking Flight
Ask 10 young officers what specialized unit they might like to train for as their career progresses and you’ll probably get four saying SWAT, three saying Motors, two saying detectives, and one—maybe one—saying "I want to be a UAV operator."
That person will probably have to invent the position for the department, standing the unit up from the ground level—both figuratively and literally. But they also may find themselves to be temporarily attached to of any one of those special units at nearly any time.