There are several different methods of doing so, but all of them required some piece of hardware that i didn't have. However i finally got around to doing some research and ended up ordering a $10 USB wireless adapter from Amazon last week. (The other option was to wait until i get my next Android phone and root it.)
It showed up last night and i spent well over an hour trying to get it installed properly. (There were two or three sets of 'helpful' instructions for how to go about the installation online, and i chose to follow the "wrong" one first, and then even when i switched to the "right" way it still took a couple tries.) However i persevered and eventually was triumphant.
The recommendation is that you cycle through the list of Mac addresses at about one every 15 minutes, i believe partly to give your 3DS time to pick it up, and partly so that you don't end up with your Mii tagged on all the relays at the same time. I couldn't get the automatic randomizer to work so i put together a simple batch script to cycle through a bunch of them and semi-randomly picked some addresses out from the list. This means that you can't just instantly grab 10 people, and you're still limited to the one tag per 8 hours per access point. So it's not instant gratification, but definitely still an order of magnitude better than anything other than a convention or a streetpass gathering.
I'd already accumulated 5 Miis the normal way, so i cycled through enough addresses to get 5 more. Remember that other post where i was amazing over the people who had armies of 300,000 in the Mii warfare game? Well now i've seen two or three people with 9,999,999 armies. In this case though i can guess how they managed it :)
After playing through with that set of 10 i set the script to run overnight. I put in more than 10 addresses because i'd noticed earlier that not every address got a hit. I'm not sure if that was because some of the addresses in the list are out of date, or if i'm getting collisions with other people who are spoofing addresses. Even 15 minute spacing isn't necessarily enough to prevent that, especially late at night when there's probably not a lot of traffic around the actual real world access points.
So if you were very lucky you could get 10 streetpasses every 2.5 hours, though i expect on average it will usually take 3-4 hours. If i really wanted to obsess about it then on days when i'm not heading up to Avalyn's place i could leave my 3DS at home when i go to work, come home to find 10 streetpasses, quickly run through all the games and start the process again, get 10 more streetpasses and run through them again before bedtime, then restart the process and wake up in the morning and play through 10 more before leaving for work.
However i doubt i'll care enough to bother doing that. Just getting 10 or 20 streetpasses a day will be more than enough for me :)