I'm not sure about what constitutes good waste or whether or not it can be used.
"Good WVO" is a relative term. If you do not have a conversion designed for use of heavy thick (or even solid) wvo then "good wvo" is clear and liquid at the ambient temperatures that exist where you drive. This may constitute as little as 15% of the available wvo depending on where you live. If anyone else in your area has already converted to VO it may already "be spoken for".
Since heavier fat or hydrogenated laden wvo is much more available more and more conversion kits are being designed to use it. Most of those conversions that are not designed to use heavier/thicker wvo can be upgraded to handle it pretty easily and economically. Generally speaking if a conversion is designed to be used in very cold weather (0°F or below) it can handle nearly any wvo you can find as long as it has been sufficiently prefiltered and dewatered.
Your best bet would probably be to convert that shortening muck to biodiesel, rather than trying to run it as WVO. Enough heat might do it, but it's a long way from ideal. Lots of trouble to filter it, dewater it, etc.
Similarly it is not difficult to collect, prefilter, or dewater high fat or hydrogenated wvo. All that is required is prefiltering/dewatering equipment designed to process this higher melt point wvo.