I disagree with Lazy; it's very doable to pluck two strings simultaneously with two fingers. It could be considered a bit of an "extended technique," but is certainly not the hardest or most outlandish thing requested in modern repertoire. A picture is worth a thousand words, so when I get a chance I might edit this answer with a video for demonstration. I actually do this often on purpose in orchestral settings that would often be taken as divisi, say pizzicato octave double stops, just because I'm bored.
In terms of technique, it helps to know the standard technique. Under normal circumstances, right-hand pizzicato is only done with the pointer finger. For the most resonant, full-bodied tone, a lot of thought has to be given to the rigidity of the finger and the angle at which it contacts the string. The performer might use some extra "tricks" to get the very best sound, like bracing the thumb against the pointer finger, and plucking near the first harmonic node of the string. In passages of rapid pizzicato—like, really, anything above 16th notes at 60 bpm—one can't be quite as particular, and settles for simply "pecking" each note.
Meanwhile, pizzicato chords are done by strumming the pointer finger across the relevant strings. If it's in forte, and the performer chooses to, this strum can be near simultaneous. At lower dynamics, or for expressive purposes, the performer could roll the chord more noticeably. Pizzicato double stops on adjacent strings would normally be handled the same way. So even with normal technique, loud ones would probably be near simultaneous.
But for truly simultaneous attack, I would simply use a second finger for the higher note. This would also be the only approach that would let us play two notes on non-adjacent strings, something like this: . Using two fingers might mean some sacrifice of that ideal, big fat tone, though honestly any loss might be slight. If there is a very long passage of pizzicato, players often choose to hold the violin like a guitar; in this case, one might pluck with the thumb as well, like guitar finger-picking technique.
- It would take some mental and physical effort to prepare these multi-finger notes. They would be better suited to long durations, or notes separated by rests, than rapid repeated pizzicati. For example, at quarter note = 60, a sequence of quarter notes would be a bit of a challenge but reasonable; eighth notes would make steam rise from my head, and 16th notes might well be impossible.
- Think about the left hand too. If notes are so far apart in range, make sure you're not causing any left-hand contortions that might be far more challenging than simply plucking with two fingers. In general, it's easy to put higher fingers on higher strings. That is, of these chords, , the first is much easier than the second.