Just think outside the box...
00 00 01 02 06 07 00 00 00
00 00 03 05 08 13 00 00 00
00 00 04 09 12 14 00 00 00
00 00 10 11 15 16 00 00 00
Now from 01 go right 1, diagonal down 3. Right 1, diagonal up 3... and keep repeating the pattern until the numbered elements are all filled in.
And I see Fell came up with some code, as well.
Pete