How can I draw text on a TImage and retain Alpha?

Still can't se why you can't draw the text to a black screen, grab it into an image and then draw them both.
Rubbish example but it might give you an idea.

Graphics 640 , 480
SetColor 200 , 150 , 150
DrawRect 0 , 0 , 400 , 400
image:TImage = LoadImage(GrabPixmap(0 , 0 , 400 , 400))
Cls
SetColor 0 , 0 , 0
DrawRect 0 , 0 , 400 , 400
SetColor 255 , 255 , 255
DrawText "Hello World" , 100 , 100
image2:TImage = LoadImage(GrabPixmap(0 , 0 , 400 , 400) )
SetClsColor 255,0,0
Cls
DrawImage image , 150 , 0
DrawImage image2 , 0 , 0
Flip
WaitKey()

p.s. the text can be drawn with a bitmap font with transparent background... I think.