Some two qubit interactions are singly sufficient for universal quantum
computation but not without the use of an ancilla. Recent schemes for universal
quantum computation have focused on hybrid physical systems using ancillae. In
them, the application of resources is shifted to the ancilla system. We
consider which 2-qubit interactions are universal in ancilla schemes where
direct connections between main register qubits are forbidden. By the use of
ancilla driven operations and repeat-until-success style random gates, a single
fixed symmetric gate can be universal be control of the number of repetitions
alone