You seem to know that the S70 XS has Elements (and does not have "drawbars", per se). There are no drawbars on the synthesizer. An Element can be used to emulate one or more drawbar footages and you can control the Element Level via front panel Control Sliders. However, Elements are not readily accessible via MIDI... ('readily available' would be via cc messages; (you can, however, access each Element via System Exclusive messages, if your controller can be programmed to send same).

What you can do...
For example, if you recall the VOICE called: PRESET 1: 103(G07) "All Bars Perc AF1&2" - This 8 Element Voice combines the 16' and 8' in Element 1 and the other 7 Elements are setup for the proper footages for a tone wheel organ drawbars (ala B3).

Element 1 = Draw 1+3 (which is the 16' and the 8' combined - the "Sub-octave" and "Principal" often are used together)
Element 2 = Draw 5 1/3
Element 3 = Draw 4'
Element 4 = Draw 2 2/3
Element 5 = Draw 2'
Element 6 = Draw 1 3/5
Element 7 = Draw 1 1/3
Element 8 = Draw 1'

Adjusting the Element level
Press the [EDIT] button in the Voice mode.
Press the Slider Function button a few times so that the lamp turns OFF. (With no lights lit, the SLIDERs function as Element Levels).
Use Number [1] – [8] buttons to select the Element you want to edit.
Use the Slider to set the output level for the selected Element.
When any of the Number [1] – [4] buttons are selected, the levels of Elements 1 – 4 will be assigned to the Sliders 1 – 4.
When any of the Number [5] – [8] buttons are selected, the levels of Elements 5 – 8 will be assigned.

You can adjust the Levels of the Elements and STORE your favorite "drawbar settings" as USER Voices. Element Level is stored in the VOICE.

Via MIDI you would need to send a specific System Exclusive message for each Element in order to control its level in real time. You don't mention what you plan on using for a controller - but the 8 Element Levels are not controllable directly via Control Change messages from an external device.

The Element is an individual component of a Voice. There are 8 per 'normal' Voice and 73 per 'drum' Voice. These are exclusive to the Yamaha system, if you will... Certainly not a feature you find in just any Midi piece of gear. Yamaha does allow you to manipulate Element Level via on board physical controls. Through Midi you need to address Elements via Sysex. If your sequencing it might be practical to add messages to change the setting, if you are looking for real time control when performing your "best bet" is the front panel CS set to Element Level (all LEDs OFF).