If you have the aux-in socket in the glovebox then you could fit one of the very cheap Bluetooth receivers that have a headphone jack on them and play what you want (for e.g. Internet radio) off your telephone?
Are these bluetooth receivers generally better quality than plugging in via the 3.5mm aux-in directly?
I ask as I was disappointed by how loud you need to turn up the aux-in with my phone (and other sources)