You could create count variable and then a custom code object to pass the count too.
Before the Get Next Item action, point to your code object and pass the count as an argument.
In the code object use a modulo calculation on the count to determine if it is an odd or even number and return ""A"" or ""B"" back to set as the tag in Get Next Item.
In VB its as simple as ""number1 Mod number2"" you will want to do ""count Mod 2"" as the remainder if divisible by 2 will be 0 which means its an even number, if not 0 then it's and odd number.
This will ensure the items collected from the queue will follow the order A,B,A,B,A,B...