can biwire cables be used on a non-biwire speaker?

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

I'm not familiar with the particular cable, but I'd feel certain that it does not contain a crossover network that would route different frequencies to one or the other pair of wires.

At most one pair of conductors might be optimized for higher frequencies, in some way, and the other pair for low frequencies. But those differences, if any, would be of comparable magnitude to the kinds of differences that cables normally make.

If the two pairs of conductors differ from each other, I'd suggest using the low frequency pair, to assure adequate gauge.

Regards,
-- Al

You're welcome! You undoubtedly realize this, but just to be sure, if you try it with your present bi-wire speaker terminals you'll have to jumper the high and low frequency speaker terminals together.

Regards,
-- Al