Here are two examples of how a Tamiya diff can be remotely locked. Both seem to involve a sliding ring around one of the axles locking the axle/shaft to the diff casing.
https://www.youtube.com/watch?v=QNNeXVwp7vA
https://www.youtube.com/watch?v=Q6foguH8UcA
The new version of the Lesu axles apparently have the same internal ratio as the Tamiya axles.