Do you have a pipe you can slip on the end of the vice grips as a cheater bar?
What about a really big combo wrench where you can slip the round end onto the vice grips and use that as extra leverage?
There's a trick a buddy showed me a couple years ago where you use two combination wrenches to greatly increase the torque for tightening or loosening a bolt. You put the first wrench on the bolt as normal, and then use the round end on one of the prongs from the open end of the other wrench (making a longer overall wrench and changing the angle that you're applying force from) and turn. It works great for tight spaces where a normal socket wrench won't fit. I even find myself adapting the principle to other tools from time to time.
Like so:
Just try it as if the red wrench were your vice grips. Might give you what you need.
Just be prepared to snap the combo wrench if your tie rod is that tight....