I have not used that procedure before. I went to do a quick Google search and nothing apparent popped up within the first couple of pages. It seems to be related/relevant to Jamie Robins Time-Varying Exposures work and perhaps Marginal Structural Models.
I will note that I saw an R program article that is only about a month old on it. You could try that program or use its source documentation to try and reproduce the approach in SAS. I bet you there is a SAS user group article on it, or perhaps one of Miguel Hernan (Harvard) programs on his University Causality page may cover the topic. Though I believe many of those approaches are related to observational data and use of propensity scoring.
Is your data observational or experimental? Also, please update your post, in that I would be interested to see where you landed in your pursuits in regards to this question.
P.S., the Analysis of Observational Health Care Data Using SAS book addresses time-vary treatments as well I believe.