Dude,

I would not recommend sending anything of that size that may be scrutinzied by US Customs.

The measures described will not avoid detection by a quick & easy x-ray.

Even in the pre-911 era things were pretty tough. I can't imagine that it has gotten any easier.

Also, they will not distinguish between salvia or real weed.
Thus, you may be considered guilty until you prove otherwise.

Play it safe & smart!