First off lets start with the basics.
1) Smell is reasonable suspicion for a search... United States v. Johns, 469 U.S. 478 (1985); I suggest your read this case to fully understand the precedence, just google it.
2) It's important to realize that there are factors that could negate the smell problem on a typical stop. Wisconsin V. Mata court documents state: The strong odor of marijuana in an automobile will normally provide probable cause to believe that the driver and sole occupant of the vehicle is linked to the drug. The probability diminishes if the odor is not strong or recent, if the source of the odor is not near the person, if there are several people in the vehicle, or if a person offers a reasonable explanation for the odor.
3) Know your rights and flex them: If you get stopped and the officer asks your permission to search DO NOT CONSENT. Also carry a camera w/ video so you can document the stop and what happened during the stop. Don't argue with the police or resist in any way if you get stopped. If you get in trouble... let your lawyer figure it out. Whatever you do don't say a single word until you have spoken to your lawyer once you've been arrested. The only words you should say upon your detention is "I want my lawyer NOW"
4) A half pound is A LOT of bud. Typically Splitting up bud is dangerous because that could provide intent to distribute (though the qty itself would probably do that on it's own... we're not talking a few grams or an OZ) In your case since it's going to be a federal felony (your crossing state lines, right?) I would just find 3 spots in your car to put it. NOT in your spare or any common areas (glove box, console compartment, etc).
5) I like the idea of putting it in the trunk, it's difficult for an officer to justify opening the trunk in almost all instances. I've been searched by police on a few occasions and they have never searched my trunk. Peel back some of the liner back there and pack the bud in bags that don't bulge then refasten the lining. If you're good with tools and such you could try to make a false bottom in the spare tire compartment or remove the rear seats and put it there. No cop is going to tear you car apart on simple suspicion.
6) You have a ricer... just make sure your plates are mounted properly, all lights work, wear your seatbelt, don't speed, and be polite and apologetic if he stops you. I'd admit to speeding with an apology and take the ticket before getting arrested for a half pound of pot.
Hope this helps.