As I understand it, in Pd it is not a code problem,
but "architecture"
issue. See e.g. here:
http://lists.puredata.info/pipermail/pd-list/2005-08/030501.html
and for SuperCollider, see here:
http://www.create.ucsb.edu/pipermail/sc-dev/2005-November/009371.html
"I don't really see a big need to run the language in a 64 bit address space,
though." - James McCartney, author of SC.