Sometimes a spark gap is used as a trigger for an exploding wire, but it occurred to me that maybe you can do it the other way around: use an exploding wire to trigger a spark gap.
If you mechanically put a thin wire partway across a near-breakdown spark gap, you will get corona discharge around the end of the wire, which will supply ions to seed the arc and tend to start forming a streamer. If that glow discharge turns into an arc, the wire will start to heat up, and if it’s thin enough, it will explode into plasma, completing the arc.
If the wire manages to bridge the spark gap completely instead of partly, then it might develop a hot spot where it touches one or the other electrode, which could melt it down to a round knob that’s too round to create corona discharge and too close to the electrode for avalanche to kick in (below the Paschen minimum). Possibly a small inductor in series with the wire (but only the wire, not the spark gap itself) would avoid this danger.