Well, certainly they can be seen in NGC7009, the Saturn Nebula. They're quite visible and detailed in my 12.5" at ~500x.
I can't recall 6826 or 7662 as having visual FLIERS, though the outer shells can be spotted, but perhaps my scope is too small.
I have seen the "ears" in NGC3242, however.
The key is to wait until the objects culminate, use very high powers in good seeing, and observe from, preferably, high altitude.
Or have a scope like Jimi's.
They are common in planetary nebulae, but mostly photographic with various forms of enhanced image processing.
If your skies are at least m.21.4 or so, and you have the seeing to support 400-700x, they would be something to look for.
Start with NGC7009. If they're easy there, try for the harder ones. You've got me on a mission, now.