I really can't understand what you're describing here. I understand that the end of the pipe is freezing, and that you will redo the job in the Spring, but that's all.
If you can extend the pipe AND increase the pitch at the END of the pipe, then you should be OK. I'm assuming you can do this PLUS you can get the pipe at least 12" off the ground. The only catch here is I don't know the rise and the run of all your pipework. You need to get those specs from the MFGR. (They have them because there are MAXIMUMS ...) If, for example, inside the house, you can RAISE the pipe, great. Then, for example, outside the house, you can EXTEND the pipe, great. THEN, for example, outside the house you can increase the PITCH of the pipe, great! You've done it!
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!