I don't see any problem with doing that, as long as the gauge is sufficient. If I understand your question correctly, one of the two pairs of conductors would be left unconnected at the speaker end. Concerns that might be raised about the unconnected wiring would involve possible antenna effects and also capacitance, but I don't think that either has any relevance to an amp/speaker interface, due to the very low source and load impedances.
The following thread addresses a different situation, but I think its conclusions are relevant to your question as well:
http://forum.audiogon.com/cgi-bin/fr.pl?fcabl&1229676493
Regards,
-- Al
The following thread addresses a different situation, but I think its conclusions are relevant to your question as well:
http://forum.audiogon.com/cgi-bin/fr.pl?fcabl&1229676493
Regards,
-- Al