One of my Swarm units can be placed atop a bookshelf, with the woofer facing up if desired.
Geddes' solution was to make a large bandpass sub with a long port which pointed upwards. The port was outside of the enclosure and extended upwards to a height of six feet or seven feet. Since all of the output of a bandpass sub comes from the port, this effectively placed that bass source closer to the ceiling than to the floor.