How can I construct a 4-ary symmetric communication channel in Matlab?

I need to construct a symmetric channel over the alphabet {0,1,2,3} similar to Matlab's Binary Symmetric Channel. I need the probability of transmission error to be p/3 and the probability of successful transmission to be (1-p) for 0<p<1.

I have not been able to find a Matlab function that meets my requirements and I was hoping somebody would know how to go about setting this up manually?

Any help appreciated.