My previous point was a supposition if Amazon had included the “Stop” action semantic extension. I was just thinking ahead 
There is no way around the recommendation I provided earlier right now.
So based on this use case, I am considering expanding the item type support for ModeController to Rollershutter (UP/DOWN & STOP/MOVE) and Dimmer (INCREASE/DECREASE). This will not resolve the issue for the missing action but would give a better control of these item type abilities.
The only issue here is that you cannot combine range & mode controllers under one single item, the same way than PowerController and BrightnessController. I just tested it and it silently fails on the Alexa side to recognize the item. So if you want to have numerical control along with using the item type commands, you would still need to use a proxy item as well. If you only care about specific positions, you can add them as modes and even give them a name.
I just want to be clear the example below will not work with the current live skill. I just wanted to know if this is something that you might consider using with your binding? I am trying to determine if I should make the change or not. With this definition, you would only have to setup a routine to send “STOP” directly to your item without the need of a proxy item.
Rollershutter Blind "Blind" {alexa="ModeController.mode" [category="INTERIOR_BLIND", friendlyNames="@Setting.Opening", supportedModes="0=@Value.Close,50=Half:Fifty Percent,100=@Value.Open,UP=Up,DOWN=Down,STOP=Stop,MOVE=Move", actionMappings="Close=0,Open=100,Lower=DOWN,Raise=UP", stateMappings="Closed=0,Open=100"]}