To speed up a shadowing process, you can employ a technique for digital tasks by asking the person to record her screen and think aloud while performing the action.
This can be easily done with tools like Loom or Descript that both have free tiers and work on many platforms.
It has a two benefits:
More shadowing sessions: You can ask multiple people to do it without being present,
Faster replay: You can play the sequence at 2X speed to see the shadowing session in a much quicker way than doing it live.
This can also work for some physical tasks. People can for example, record themselves using their smartphone if they are stationary or can use one hand to do the task while holding the smartphone in the other hand to show what they are doing.