I don't know if a Rechungpa sadhana exists or not, but Changling Rinpoche is the current lineage holder of Rechungpa's teachings, so if anybody knows the answer, it's probably him.http://en.wikipedia.org/wiki/Changling_Rinpoche
Rinpoche taught a "Rechung Gar" Retreat last summer, but it's not clear if it involves visualizing Rechungpa or not.http://www.lotusspeech.ca/sproatregister.php
I also remember a long time ago reading about a Kagyu tradition which had a six-year Mahamudra retreat in order to pass on Rechungpa's teachings. I forget whether it was this Rinpoche or another one. If I remember correctly, they were trying to set up a retreat center in New York, but I can't remember and I can't find the webpage anymore...
I guess the topic of this Rechung Gar (Rechungpa's camp) retreat was his 6equal tastes. At least in TBRC there is no guruyoga on Rechung composed by himself. There are some writings on Vajrapani and medicine. Not much of anything else, although of course one could not consider TBRC an ultimate source of Tibetan texts. I will check what they have on the previous Changling Rinpoches, maybe one of them composed something.
Edited due to failing internet connection.