Outdoor thearer heating options

Well since the weather isn't going to help, I'm wondering if technology can come to the rescue and get the drive-in going earlier. What sorts of ways have you found to warm your guests without ruining the experience? Late last year we tried to heat 20 people with a small fire pit, but only the closest were happy. In addition the seating arrangement made movie watching difficult with us all in a circle. So this year begins searching for an alternative. There are propane heaters, and quartz infrared patio heaters that I've found so far on the web. The idea of an invisible electric heat source sounds promising, but I'm looking for your thoughts to prove or bust this myth.