Hi,
currently SMD pad size is limited at about 0.5 x 0.5 inch. So you have to use a smaller SMD for connecting the signal and use a polygon over the SMD for the whole copper area. Or you can combine several SMDs as you already tried to. Currently I don't have better solution. I'ld prefer to have some SMDs and live with the DRC errors which you can approve in the layout.
I am pretty sure that this issue will be solved in future. Probably with the XML based data structure in EAGLE.
Regards,
Richard
For a very large SMD pad, this time, I am using layer 29 Tstop to define an area where there will be no solder mask (defined in the part).
In the board editor, turn on layer 29, then "polygon gnd" and draw a polygon over the Tstop area uner the part. (where gnd is the net to solder the part to) You will want to turn off layer 29 before you do a DRC or you will get many errors as many parts will have layer 29 over laying pads.