Found this on the scion forums... but if you have a grill SECURELY installed to your Celi - this could also work out quite well for you too
Items needed: (items listed can be found at Lowes)
2 - 4 or 5 inch 3/8ths carriage bolts (I used 5 inch, maybe a little longer than needed)
4 - Large flat washers ( I covered one side of each with vinyl sticker for scratch protection)
2 - smaller washers (fender washers ?)
2 - 1.5 inch steel Spacers
4 - 3/8ths nuts ( I used two regular and two with the locking plastic ring inside)
OPTIONAL: Mounting bar (I used some flat aluminum, NOT fun to work with)
Mounting bar is optional because you could just use the bolts thru the License Plate
holes and mount it straight up that way.
Drill holes in the mounting bar and dremel or file holes to accomodate square part of carriage bolt head. Insert carriage bolts, put small washers on the bolts. Follow with steel Spacers and regular 3/8ths nuts. Tighten nuts to hold carriage bolts and Spacers in place. Add one large washer to each bolt. Insert bolts thru honeycomb at desired location. Place large washer on each carriage bolt behind honeycomb, follow with locking nuts. Tighten deez nuts until it sandwiches the honeycomb between the large washers. Add additional nut to lock if desired.
You should end up with something like this: