Hmmm . . .
Place your video on Track 2
#1 - Put a SOLID colour ABOVE your 2 Events onto Track 1. Initially You're gonna have to chose solid WHITE - you'll see why ..
#2 - Apply LENS Flare to this solid colour OR the Track Header and bring its colours to 132 132 132 - kinda soft dark grey - yeah?
#3 - Mute Track 2
. . here comes the possible trick . .
#4 - Apply Chroma Key to Track 1 Track Header
#5 - Click on the CK Track Fx and now using the Colour Picker drag a range that includes the BACKGORUND Colours of the Lens flare - the soft dark grey.
#6 - With the "SHOW MASK" engaged, adjust the Low and High threshold until you achieve as mush of the Lens flare "elements" as you wish.
#7 - Blur until the lens flares are Chroma Keyed to your satisfaction
#8 -DeMute your other tracks
#9 - Apply Gaussian Blur and adjust to your level of bluring. - You may not even NEED this further GBlur as your CK-ing bluring might just float yer boat!
There maybe other ways to do this but this is my attempt. I did it this way as I was thinking an EMPTY event is just that - empty. It hasn't a reference with media or the like in it. Applying an FX, I can't see how that would take hold? And yes I liked your approach too! However, realizing that I actually NEEDED something within the event I gambled on a SOLID colour. I then also realized that if I was to use my possible approach - Chroma Keying-out - then I sure was needing a colour that was NOT part of the lens flare Fx - so that meant a grey.
So to recap:
A] Apply Solid Colour Above Events and Apply Lens flare Fx
B] Use Chroma key to Remove Solid color background to leave lens flares "suspended" on transparent background.
I've used Chroma Keying for ALL sorts of wheezes and tricks. It
AINT just for Superman!!
Hope this helps
Grazie