Ok, i understand the problem better now. I once had a similar bluring for a depth of field effect implemented and its performance was ok...but it looked horrible and i never went public with it. I also had a postfiltering implemented (like the Voodoo2 did it) but i decided to remove it in one of the latest versions. Performance for this filter was ok too. So it's definitly possible to do this in reasonable time.
The problem is, that working with the pixels-Array on the application side works only if Java2 (i.e. a BufferedImage) is used. In Java 1.1, a MemoryImageSource will be used and that's "blind" for changes you may apply to the pixels-arrays. That's why the docs for this method suggest to blit the pixels-array back into the framebuffer....but that's even slower.
If you don't care for Java 1.1 support, just optimize your bluring routine and you are done. If support for 1.1 is important, adding the bluring into the engine's core would be the better solution. In this case, just send me your bluring routine and i'll add it somehow.