No. The limitation is the Memory Interface Width.
The GTX 460 768MB GDDR5 has a Memory Interface Width of 192-bits.
The GTX 460 1GB GDDR5 has a Memory Interface Width of 256-bits.
The GTX 460 2GB GDDR5 has a Memory Interface Width of 256-bits.
You would be able to run a 1GB and a 2GB card in SLI though.