Also, an interesting article here http://www.soundonsound.com/sos/jan07/articles/mixingheadphones.htm about mixing with headphones. Biggest issues mentioned are 1) lack of bass response (addressed by comparing to reference material, and listening on different sources, and higher quality headphones), and lack of cross-talk (which is mimicked by those plug-ins, and I think you can even “build one” within Cubase).
Direct answer to your question: there is softwear to simulate the “head masking” effect, and the fact that with non-headphone listening, we hear some of each channel in each ear. The article Includes links to plug-ins that are supposed to do that.
They mention Sennheiser HD650s and AKG K 701s by name as good choices. Article is 3-4 years old now, I’m not sure how to find out what the replacements are. They are both open-backed, which means the sound leakage might make it hard to track with them - but hey, a cheapo pair ought to do for that!
For me, the question isn’t “should I mix on good headphones, vs. on excellent speakers in a perfectly treated room?”, but rather “… vs. with average speakers (at best) in a bad room …”