It is really simple, and combined it with the advanced mechanic of rimming.
And the first time a speedster hits a gapper and you watch her round 1B take 3-4 more steps before you have to move, you really appreciate it. Not to mention the 4th time.
No other changes to standard mechanics.
For plays at 1B, you are not exactly in the standard calling position you would be in from "A", but you are in the exact same position you would have been in had there been R on 1B and the play was made at 1B.
No calls were any harder to make because of it.
True, you don't get the best view of F1's feet, but if you suspect something is going on, just slide back to "A" for a pitch or two.