No, you can' t fill in blocks
Unless maybe you have the resources and can do the math (say Your area was 84 x 56 blocks, you'd do 84 x 36 = 3024, then divide 3024 by 64 = 47.24, then you'd need 48 stacks.) Then show an admin that you had 48 stacks of whatever block, and they could to it for you then delete the blocks.
Probably not though