You can fake a tune mode in the LD-5 by switching the CW key type to straight key, and either using a key held down, or make a small 3.5mm jack shorted to simulate a keydown situation in the ‘key’ jack.
Since I have a key with me most times I’m operating, I just use the key method, then switch back to iambic mode.
73
-Thom
w8tam