Removal of plus sign from variant pricing

Hi,
We make use of variants with additional pricing compared to the main product. This additional pricing is usually positive.

However, we now have a situation where we would like to have a variant with a negative price i.e. a discount.

Hikashop manages this perfectly well (see attached image) but the +- in the additional price display is a little confusing.

Is there a way to turn off the + sign in this particular display, so that if the additional price is positive there will be no sign but if the additional price is negative, there will be a - sign?

Regards
PhilP