different amount of blood consumed per command? nice idea, but, as 
pointed out previously, players would use the largest consumption 
command.   As far as I know, vamps can't get over-full on blood, so 
using the max command would make sense.  The only way it would be a 
decision call would be if the composite command took the same amount 
of time as the combined individual commands.

that is, 

drink rod
drink rod

... would take up the same amount of time as

gulp rod

... for example

******

Then, if a person only needed a little blood, they could just

drink rod

... while, if they were always using the max command, they'd go

chug rod

... and it would take same amount of time as 4 drinks, for example.