In reply to Ethan. Great question! PROC OPTEX supports multiple variables. For example, if you want the groups to have patients that have the same average diastolic and systolic blood pressures, you can write:

%let Var = systolic diastolic; /* names of multiple covariates */
proc optex data=Treatments seed=97531 coding=orthcan;
class Trt;
model Trt; /* specify treatment model */
blocks design=Units; /* specify units */
model &Var; /* multiple covariate means will be approx same */
output out=Groups; /* merged data: units assigned to groups */
run;