I think there is a setting for that. It has been a while since I tokenized the machine. Try different credit styles, one of the should work as you want it to. It's this option. Foster did this with his machines, maybe he will chime in.
Credit Type
Selection <0> [5] The credit type can not be changed if credits are accumulated or if the tournament option is enabled. Options are Standard Euro credit {1}, Euro noncredit {2}, Nevada-style credit {3}, Nevada-style noncredit {4}, Lottery-style credit {5}, Semi-Euro credit {6}, Token credit {7}, or Semi-Euro credit II {8}.