Disclaimer: I have not done this yet. It’s on my list for the upcoming season.
According to John Moody in his The Elderberry Book
I paraphrase: Choose new young softwood branches that are just turning from green to brown, cutting the branch into 5-to-6-inch pieces. Remove all but the two topmost leaves from each segment. At this point, you can root them in water or soil. The plants take about 12 or more weeks to develop sufficient roots.
Will you be traveling by car or plane? This may change how to handle the cuttings. If by car, I’d put them in pots, multiple cuttings per pot, keeping the soil very moist, out of direct sunlight. If by plane, I’d put them in a Ziploc bag, the ends without leaves wrapped in a very moist kitchen-sized towel. I’d pack it in my carry on and avoid crushing them.
Also, if the leaves are large, I’d cut most of each leaf off. Akiva of Twisted Tree Farm
has an Article about propagating mulberry trees
. I think his point about cutting the leaves would be applicable to your situation with elderberries too.
When you get them home, keep them out of direct sunlight until well-rooted. Setting up a misting system would be ideal, but keeping them in a self-watering system may also work. I’d be tempted to move them to a bucket of water in the house, guaranteeing them attention until rooted.
Another option, would be to dig up a few new root suckers from the base of the plants. I have had success with transplanting young plants propagated by the birds. Theese may not be true to your desired variety though.