Sorry for the late reply. How are you making out with this issue?
If you still haven't worked around this or would like to in the future, below is some steps to accomplish what you want in Lightworks. It has quite a few steps, but once you set it up you can save it as an effect and apply it later just like any other effect. Attached is a screenshot to see what it looks like before proceeding.
Add 2 video clips to the timeline (one above the other)
Apply a DVE to the top clip
Click "Video Routing" on the panel that appeared
Drag a "Masked Blend" (Mixes) and "Simple 2D Shape" (Mattes) effect out from the list on the left
Click the node point (colored in half-circle) on the right-side of the DVE effect
Now click the FG node point (hollowed out half-circle) on the "Masked Blend" effect
Disconnect the DVE BG node (for V2) and connect it to the BG node on the "Masked Blend" effect
Connect the "Simple 2D Shape" node point to the Mask node on the "Masked Blend" effect
Your Routing panel should now look like the attachment
Open the "Effects Configuration" panel and adjust the effects' parameters until the output looks like what you want
When you're happy with the look, click Save at the bottom
Granted a parameter on the DVE effect would be much easier, but for the time being you can use this. There are a lot of steps but it isn't really that involved and it's probably easier than loading everything into Fusion and then back into Lightworks. Good luck!
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