CorelDRAW Graphics Suite X5 :: Resizing File Or Objects When Exporting On TGA Format?

I am drawing pictures for the Second life game. I need that the file I export to  be exactly 512 X 512 pixel, and TGA format. Of course, the objects in the picture are small, and don't use al the 512X512 space.But even when objects don't use all the space, I need my "small objects within the 512X512 size file.

Although my picture is, in corel draw 512 X 512, when I export to TGA  , I have no the good results.I use yhe File/export/menu and define TGA Bitmap for format. 

On the following menu,

if I click on "Maintain original size", Objects remains  with original size, but the file size  is reduced to fit around the objects..

If I click on "Maintain aspect ratio",, I can fix the size file to 512X512, , but the objects are streched to fill the 512X512 file.

The only way I found to avoid resizing  is adding  a 512X512 transparent object on the background, but I wonder if there is a better way to do it.