That's insane.
Why have a shuttle, which costs a lot of money to build, maintain, and operate, which has a weird and complex service pattern with the possibility of causing delays, when you can just have a pedestrian tunnel which is functional 24/7 365 days a year. The train would only be able to get their maybe 90 seconds faster on a good run considering the curves and switches that it would need to traverse, not to mention the time spent waiting in the station for it to come.