Option 1: You will not be able to install SP14 with out UI
only thing you will need to do is upgrade your stack until SP12 first usinf SPAM/SAINT
and then generate stack xml for SP14 which includes UI files and run SPAM/SAINT
or
Option 2 : run the upgrade thru SUM
In my case I went ahead with option 1 because I had some issues with Java and had a hostname conflict with solution manager Disaster recovery system, I have to force some changes in the hosts file entry which points to the DR system but SUM tool is not liking it
If I remove that hosts file entry then Java is not geting started
Since I don't want to spend much time in that as I was busy in some other things and I went aheas with SPAM/SAINT which how ever took good amount of time 