"You could parallel them and read one which would "more or less" show 1/2 the current flow."
Yep TomW is right , but the reason I didn't mention it is that the resistance of the shunts is so light , you would have to be really carefull with the splits to parallel, and the joins . I think the deviation could be much higher than expected from the extra wires etc..
This is 4 connections (split to the shunts, join out... shunt to meter join from shunt, and split back) ....
Although you could calibrate it with another meter to get a reference..... still a pain , as you would have to do mental math each time you looked at the meter.