Grab some cheap green radiator coolant down at the local auto store, fill a jar with the fern cuttings, and then let the jar full of coolant soak for 4-6 weeks (or more). I just took out a batch that I set to soak around 6 months ago (forgot they were at the back of the workbench!). When finished the preserving time, pour out through a sieve, and give the fern a good rinse with water. This will help the fern preserve shape and structure. I then lay the pieces out on a scrap of card and hit them with a light coat of suitable green spray paint.
The same preserving process works for most moss, lichen of small plant samples you may find.
Hi Woodie...not sure that I know all the cool tricks...still haven't managed to fool my kids with the old "pull a penny out of your ear" trick as yet! But I do tend to surf a number of forums and see a lot of ideas and techniques that oneday I might get around to trying myself.
I thought with the sage brush though, they were normally sort after for the dried and knarled looking tree trunk appearance, and were more about being dried stem cuttings rather than preserved in the coolant (but I've never used the sage brush, so don't quote me on that one).