How to set custom start position between grid lines with “snap to grid” enabled

I am using a slider that has the following characteristics:

min. value = 1 ; max. value = 6; "snap to grid" enabled

The slider does not have a neutral point, however I would like the start position of the slider handle to be at "3.5", for it to be midpoint between 3 and 4 and not influence respondents (whilst retaining "snap to grid" and without adding decimal places).

Is there are away to do this?

I have tried fixing this using the below code, for the first question in a series of sliders:

Qualtrics.SurveyEngine.addOnload(function() {
this.setChoiceValue(1, "3.5");
});

I expected this to work. However the handle automatically snaps to a starting position of 4 (and is also in bold colour indicating an active choice as opposed to a default starting position).

Any help would be really appreciated