Is there any way to get houses up in the showcase, other than streetpassing another player who has their 3DS set so the info can be sent? I'm never around people who are doing this. Is there an alternate way?
If you can find a Streetpass Relay you can get streetpass data from the last 6 individuals to pass the relay. Nintendo implemented these relay stations specifically for this situation.
Sadly, this is the only way you can get more houses in the showcase. You can see if there are any Nintendo Zones near you. Since Nintendo has implemented the Streetpass Relay you will have a better chance to Streetpass others.
Another alternative is to create your own StreetPass Relay Station with your wifi router at home.