the easy way around that is to get a small mixer like a Mackie 802 or 1202 and use that to manage inputs to your DT.
A more challenging approach would be to hack together a Raspberry Pi into a USB host. There are tutorials out there explaining how to do that with MIDI, but my experience with Linux audio has largely been disastrous due to lack of patience. 
The iPhone/iPad Camera Connection Kit turns the iOS device into a USB host, which is why you are able to make audio connections over USB between the iOS device and Elektron device. An MPC or a 1010 box can also be a host, but neither of those make very good portable recorders.