Yes—using your existing Cactus V5 transceivers, you can manually fire the off-camera flash remotely. The V5 has a test button, so if one transceiver is attached to the flash and the other is in your hand, pressing the test button on the handheld unit should trigger the flash.

Another possibility is the flash itself: some flashes have a stroboscopic/repeat mode that lets you set multiple flashes with a chosen interval. If your Starblitz supports that, it may be the simplest way to get repeated bursts during one long exposure.

If not, a basic manual trigger works by momentarily closing the hot-shoe sync circuit (center contact to ground), which is essentially what a test button does. So an off-the-shelf solution does exist in your case: your radio triggers already provide it.