I have just altered vm so the next release (week or so) will allow a board property of:-

build.linker_relaxation=false 

in the current build for arduino versions below 1.5 the relax is forced on for the 2560 chip or if build.linker_relaxation=true

so that doesn't help you right now, but you can try build 1305.21 from our beta channel along with arduino 1.5.2

I notice in 1.5.2 the relax option is not hard coded, it is set using the boards.txt and platforms.txt in the ide/hardware/arduino/... folder

1.5x is beta but I think it works okay for avr chips so you could give it a try and create your own custom board def. do you know how to do that?

Attempting.. I have 13.05.21 and Arduino 1.5.2
The VM/VS environment can't find the libraries (e.g. <Ethernet.h>). How do I resolve this?

Thanks.
I got it compiling with 1.5.2, without removing the relax flag, hopefully it means the bug in pointer relaxation (in the linker) has actually been fixed.
To compile, I had to edit the various .cpp's in the Ethernet lib so they would find w5100.h and socket.h as utility/w5100.h and utility/socket.h; or I probably could have copied socket and w5100 back a level into libraries/Ethernet. I guess you've encountered that..?