Bex constant selection on multiprovider with several infoproviders

Hi Gurus,

Is there any way to use constant selection on multiprovider with 3 infoproviders,

1. We have 3 keyfigures each one coming from different infoproviders. We are getting the query output in 3 different lines,we used constant selection on 2 infoproviders and able to merge the output? But not able to use constant selection on all the 3 inforproviders at a time?!

Can you suggest any alternative solution on this issue?!