Couldn't you just say "I'm meeting up with a few friends in (not from) [city] to go sightseeing and explore the area" ? That seems like it is entirely truthful, plays up the non-sketchy aspects, and exposes you as a tourist who will spend money, and since you're meeting other people the lone traveler aspect is diminished.
If pressed as to why you're not carpooling, you can say "We're coming from all over- it was easiest for us to meet here"- which is once again entirely honest, and logical, especially if you're in the Ontario/Quebec part of Canada- no sense in a roadgeek from Kentucky to drive to Maine first for a Toronto meet!
It is an annoying barrier though- I've been having trouble convincing myself to clinch highways in southern Arizona just because I don't like hassling with the checkpoints- I've never had any issues with them, but I always worry that next time will be the time. I don't really know how to truthfully explain to CBP why I'm on SR 286 right by the border in a really rural area along a major drug smuggling route- "Well, officer, I'm only here because I'm driving every mile of state highway in Arizona, and this is a state highway in Arizona." In fact, I'm not even really sure how I'd lie about it- there's just no good reason for a middle class white kid in Tucson to be in Sasabe at this point.
As far as meets go- I can try to make any that might occur in Texas or Oklahoma, but anything else is probably too far out. Come 2013, I'll be in the road meet game. In fact, 2012 looks pretty bad for me on the driving front- I'll probably concentrate all my resources on finishing the AZ state highway system and getting the hell out of this place as soon as I graduate next December.