This is very handy for quick analysis of stuff that's not L2 adjacent with an analysis station.
First, create a local mirror session:
mirroring-group 1 local
Next configure an unused physical interface for use by tunnel interfaces:
service-loopback group 1 type tunnel interface <unused-interface> port service-loopback group 1 quit
Now configure a GRE tunnel interface as the destination for the mirror group:
interface Tunnel0 mode gre source <whatever> destination <machine running wireshark> mirroring-group 1 monitor-port quit
Finally, configure the source interface(s):
interface <interesting-source-interface-1> mirroring-group 1 mirroring-port inbound interface <interesting-source-interface-2> mirroring-group 1 mirroring-port inbound
Traffic from the source interfaces arrives at the analyzer with extra Ethernet/IP/GRE headers attached. Inside each GRE payload is the original frame as collected at a mirroring-group source interface. If the original traffic with extra headers attached (14+20+4 == 38 bytes) exceeds MTU, then the switch fragments the frame. Nothing gets lost and Wireshark handles it gracefully.