Surely, it can be done.
The easiest method would require that your compound be turned parallel with the lathe Z axis. This means your plunges would be straight in at 90 degrees.
So you can cut one thread with the compound dial set at zero, then crank it along one thread pitch to cut the other one. Remember the pitch is half the lead in this case, so if you are cutting a double start 8 pitch thread, then each thread's lead is 4 threads/inch, but the difference in the start position for each thread would only be .125"
In actual practise, if you don't like the straight in plunge, you can jockey the compound back and forth a wee bit for alternate cuts, to lessen the chip load per cut. Keep track of the backlash and always end with the compound right on the zero mark, so you know that you haven't lost position.
The other method involves studying the gear train at the end of the lathe. Hopefully, you will find the drive gear off the spindle or the driven gear on the quickchange has an even number of teeth. So you mark one tooth when done the first thread. Slide the gear off the shaft, and turn either the spindle or the quickchange enough to turn exactly one half of a turn, so the marked tooth will now go on in the opposite position to what it did before. This should give you the new start position for the second thread.
Edit: Oh yeah, lathe dogs and faceplates, forgot about that, LoL
