I'm actually just in the process of implementing this for version 5.1.
The approach is to define the tidal stream speed and direction for each hour, from 6 hours before to 6 hours after high tide. This is done for springs and neaps (with the mean range of springs and mean range of neaps being defined as well).
Bridge Command will interpolate depending on the current tidal range, and the time relative to the nearest high tide. This should match the 'Tidal diamond' approach used on UK charts. You will be able to define the tidal stream in as many locations as required, with and Bridge Command will interpolate between them.
I've implemented this already, but need to complete thorough testing.