you can try this:
I had the same problem few days ago when installing a new wallet in a mac with yosemite and the bootstrap don't worked to me.
I solved by copying and pasting the XST files that was in my other mac with osx mavericks.
I put available on dropbox the actualized blockchain (blk0001.dat file + txleveldb folder) working on yosemite https://www.dropbox.com/sh/hhr92ot8r0k18vx/AAAXlMoBts1Tz_sFd5Z1Nw9La?dl=0
If the tutorial posted by MR1 don't work also to you, try this:
-Close your wallet
-Go to "user/library/application support/StealthCoin" in your mac, delete everything except "wallet.dat"
-Download and open the folder "XSTblockchainOSX" from my dropbox and copy and paste the file "blk00001.dat" + "txleveldb" folder in your folder "StealthCoin"
-Restart your wallet and wait less then 5 minutes
Im a bit paranoid about doing this is there any risk of hacking etc?
If you are so paranoid, don`t download it man!