I think I solved that problem, after doing a few searches and experiments I came up with a very convenient solution that is now working for me quite well.
Now let's assume you have the SculptyMap you exported from Zbrush
The Sculpty map is in "bmp" format
Change the sculpty map into "png" format using any 2D editing software
Get a free software called "Sculptypaint" It's a java software and available on this link http://elout.home.xs4all.nl/sculptpaint/
Now after downloading the software open it and drag and drop your sculptymap.png into it
It will give you couple of choices, chooses "Load as a new Sculpt image (.png)"
This will load your sculpty, you will notice that your sculpty far off or unsymmetrical to the main axis
Now the point is to center your object so that its in the middle of the axis
On the right side of Sculptypaint underneath the sculpty map click on "Select All" this will enable you to move all your sculpty into position
Click on Translate x or y or z till you center your sculpty onto the axis so it's almost balanced
When done, click "Save 64*64 Sculpt Image" on the top left side of the window
It will save the image in the SculptyPaint Folder so dont look anywhere else for it
Now go to second life and upload your SculptyMap, but the next step is important
When you upload the sculptymap you will find it distorted, Dont panic. What happened is that the sculpty paint has enlarged your sculpty to fit in it's bounding box.
All you need to do is to resize the sculpty manually, but in the end you will get a skin tight bounding box around the sculpty.
Note, it might be a little extra work resizing and so, but it sure is worth it and it's not a tough job either.
Hope it works for you as well. cheers!