Producing a standard from anything generally involves a multiyear process of staking and cutting back. Check pruning books with diagrams to get a visual. Not sure this elder is one that lends itself to training as a standard, even naturally treelike ones such as blue elderberry - which I have seen over 50 ft. high - often have a sprouty, weak-wooded appearance. "Use only vigorous species such as S. sieboldiana to train as standards, clearing the stem to a height of 3-6ft (1-2m). These vigorous elders tend to produce numerous suckers and shoots on the clear stem, which should be removed promptly. Elders are generally short-lived, in spite of the rejuvenating effects that hard pruning can have. Old and neglected specimens are best replaced." --C. Brickell/D. Joyce, PRUNING & TRAINING (DK)

Yes: it is liable to be too big. If happy, will blow right past 5' in no time. The one here certainly did this. You might try it anyway, to see how it behaves on your planting site. Cutting tallest stems down low periodically, leaving the rest to control height might be possible. But elders shoot up so fast that re-growth may rapidly exceed the 5' each time. If you want full production of flowers and fruit spread throughout the bush heading back too tall stems may perhaps interfere with this - or produce a bit of an unattractive stubbiness. Try searching sambucus pruning for additional discussion. Does not have to be about this particular one to apply.

You might have better luck in getting replies by posting on a forum in your part of the country. I certainly hope you get some answers after all this time.

Yes. I've seen a ref. to it from the nmsu ag site: http://cahe.nmsu.edu/ces/yard/1997/091597.html but as to the best way, someone else might have the answer to that. You might want to contact the lead horticulturalist @nmsu, curtis smith. He's a great contact for gardening questions in general for new mexico.