[gmx-users] Pull code using two reaction coordinates??

[rversace at ccny.cuny.edu]

Hello everybody:
I am trying to perform some PMF calculations using the pull code with a spring (umbrella sampling) but using two reaction coordinates (E1 and E2) between four different groups (r1,r2,r3 and r4). 
All the examples and tutorials that I found so far on the web, only mention PMF calculations for one reaction coordinate (E1) between two different groups (r1 and r2). 
Is it possible to perform the calculations using two reaction coordinates at the same time or should i do two different individual calculations or there is something more that i should do to achieve it?
I will appreciate any help.
-Rodney