You're not supposed to park at Poly the whole time you're at MK (I think the time limit for visitors is 2 hours).
It is VERY easy to get to the GCH from the TTC, a very short walk (maybe 7 mintues, if you walk at a comfortable pace, we have done it faster). I suggest you park at TTC and walk to Kona, then you won't have to think about it.
Enjoy!