Knold,
You risk falling into a common trap of trying to make V1 (one of many aspects of flying which fall into this category) operationally far more precise than is warranted by the technical reality.
If there is plenty of spare runway, the reality is that a modest speed overrun probably can be accommodated.
If the runway is accel-stop limiting then there is scant pad .. especially for pre-A/L 42 certifications. Add this to touchdown zone contamination at the stopping end .. grease ... oil .... did it rain a bit half an hour ago .. etc., etc. .. and you are near guaranteed an off-the-end event.
Risk assessment and minimisation in the real world is the aim of the game .. the certification gives a baseline from which to work but makes no guarantees unless the boundary conditions can be replicated in toto.
So far as calling V1 is concerned, it should be little more than "hey offsider, my ASI indicates that I am passing the precomputed V1 .. hopefully yours says the same ?" ... the other pilot should have been keeping a very close eye on his ASI throughout the takeoff. Hence there is little point in doing other than saying "V1" relatively normally .. but timing, I suggest, should be such that the verbiage is completed by the time that the needle is at the nominated speed.... and let's not get too bogged down by IAS/CAS concerns ...