Congratulations Luchha!

It's very simple. Just print in your invitation cards "Gifts are appreciated but cash prefered due to logistics". If you think they cannot understand that, then be direct and print "Cash Gifts Preferred". And tell your parents that when they are inviting the guests, they can discretely mention the difficulty in carrying all the gifts back to US. Hence, cash gifts would be welcomed.

My gift for you and your wife-to-be is this:

"What is the best gift you ever received? Better still, what is the best gift you ever gave? Perhaps you will recall that in each instance, the best gift was one that was tied with the heartstrings of the giver, one that included a part of self." - Wanda Fulton