I'd break it down into pieces, and as damfino said, do it slowly (so slowly it's easy, ideally.)

Here's the pieces I see from the description (take what's useful from this and pitch the rest. I'm a raw beginner, so there might be better ways to break it down.)

• A down bowstroke that's about 3 times longer than any one upstroke note, which means it needs to be three times faster. Practice just that (open string, no fingering). Fast downbow, upbow three times slower.
• Slurring the notes: play just the upbow notes, slurring them as in the music. This will probably be the hard part, because your body wants to do something with both hands if you're trying to do it with one. Remember, playing violin is like patting your head while rubbing your stomach (or, for more accuracy, while riding a bicycle, while holding a cat in your lap that's unhappy about all this motion, and debating about how much claw is needed for safety.)
• Play the downbow note, making sure your pressure and such isn't getting excessive in the rapid motion of the bow.
• Play (at whatever speed makes this easy to the point of being boring) both the downbow note, then the upbow notes. Just do each one in order, don't worry about them flowing smoothly yet.
• Finally, play them smoothly (still ridiculously slow) so that the entire four notes is a unit.
• If there are multiple such beasties, join them together the same way as you did the two sections of the four notes. Get the entire phrase easy to do as individual pieces, then work on playing them as one long, smooth, unit.
• Start increasing speed, preferably at a rate at which it's always easy and it bit boring. Keep doing that until you're 10-20% over normal tempo.
• Incorporating it in the song should be easy at that point.

Hope this helps,

Charles