Compile GCC to NASM compatible ASM.
 

Is there an easy way to make the assembler output (-S) be compatible with NASM?
Is there a free (preferably in the ubuntu/debian repositories) converter if the above is no?

intel2gas -g ? .. not that I've tried it

Umm, What/How do I do that?

Output from gcc -S is gas (GNU Assembler) format, to convert it to nasm format you can try http://www.niksula.hut.fi/~mtiihone/intel2gas/