Homebrew PCBs

Two things that can help with what you are attempting to do, 
select "drc" (Design Rules Check) then click the "Restring" Tab, 
Under PADS Top & Bottom, change the % (percentage) to a larger 
number, then click "Apply" button. 

I would suggest that you save your file under some sort of alternate 
file name before testing these procedures. 

( Extracted text from the Eagle "Help.Pdf" file )

Restring
The Restring tab defines the width of the copper ring that has to 
remain after the pad or via has been drilled. Values are defined in 
percent of the drill diameter and there can be an absolute minimum 
and maximum limit. Restrings for pads can be different for the top, 
bottom and inner layers, while for vias they can be different for the 
outer and inner layers. If the actual diameter of a pad (as defined 
in the library) or a via would result in a larger restring, that 
value will be used in the outer layers. Pads in library packages 
usually have their diameter set to 0, so that the restring will be
derived entirely from the drill diameter.

( End extracted "Help.Pdf" text )

The second item is as follows, if you don't have these files they can 
be downloaded from the Cadsoft website and saved in 
your "X:\\\Eagle\ulp" directory. 

From the command line in the Board layout window "Run drill-aid.ulp"

Open the files with a TEXT Editor and read the headers . . .

drill-aid.ulp
Limit drill diameter of pads, vias and holes for easier manual 
drilling. Draws small circles in layer 116 inside the drilling of 
pads, vias and  holes, which should make it easier to center the tool 
while drilling the board manually.

drill-aid-delete.ulp
Allows selective removal of circles in layer 116 inside the drilling 
of pads.