Actually, the odds of each side are the same, so just make dice explode on 5 or higher on a D6, its not aesthetically pleasing maybe but its mathematically the same thing? CRL is an api script you can program to fire a token action from an archived sheet whenever a critical is done via chat or a fumble. As well as other easily parseable character sequences. it wouldn't work after thinking about it cause it won't know how many crits and how many failures. I'd just make a custom dice and manually roll, or just explode on 5's and higher.