There is a way that you could do it with vector variables. Something like this may work, if you want an 80-20 split (anyone, please correct me if I am wrong.)
01 wait-time 2 secs hearing ringback
02 goto step 7 if A = 4
03 set A = A ADD 1
04 route-to number 1 with cov n if unconditionally
05 goto step 2 if unconditionally
06 stop
07 route-to number 2 with cov n if unconditionally
08 set A = none ADD 0
09 stop
10
11
If A=4, then you have received the first 4 calls to number 1, then the 5th call, would route to number 2 and reset the counter back to 0 to count up to 4 calls again.
If you are going to do this, you must remember to set the vector variables.