I won't say this is right or wrong .... but, I used to own a 24' w x 36' garage with standard 2x4 trusses on 24" centers. The garage doors were on the 24' end of the building so the trusses were essentially 24' long. I was able (with some difficulty) to maneuver a pair of 12' 2x4s up onto the top of the bottom truss chords; ie., the 12' 2x4s were laying perpendicular to the trusses and on top of the horizontal truss members.
After getting the 2x4s up into the trusses, I spiked the 12', 2x4s together thus making a "beam" 3" wide x 3-1/2" high. The 12' beam spanned six trusses thus distributing load over the 6 trusses. I wrapped a chain around the center of the beam and hung a chain hoist from the wrapped chain. I never went crazy with trying to lift anything super heavy, but I never had any problems.
You could even add a 3rd 12' 2x4 either above or beneath the first two (laying flat, not on edge) and get even more strength at your lift point. Or, use 2x4s longer than 12' but good luck trying to get them threaded up into the trusses!