Well... let's see what can be done.
Maybe some of my floating candles on the cake...
Ask Uncle Deadly to come and play the organ for when we sing Happy Birthday to Grover...
And redecorate the third floor common room and parts of the dorm house with bits of blue fur...
Yes, the bits of blue fur would blend nicely with the Halloween decorations. Hope that's OK with you Grover, let us know if there's anything special you'd like.