Pie Chart JSON Theme label position Prefer Outside

I have been trying to get the JSON syntax for the labal position to be prefer outside.

The following works to set the "position" option to "inside" or "outside" but it doesn't work for "Prefer inside" or "Prefer outside"

WORKS:

"pieChart": {
"*": {
"legend": [
{
"show": false
}
],
"labels": [
{
"bold": true,
"backgroundColor": {
"solid": {
"color": "#000000"
}
},
"position": "outside",
"labelStyle": "Category, data value, percent of total"
}
]
}
},

Doesn't work

"pieChart": {
"*": {
"legend": [
{
"show": false
}
],
"labels": [
{
"bold": true,
"backgroundColor": {
"solid": {
"color": "#000000"
}
},
"position": "Prefer outside",
"labelStyle": "Category, data value, percent of total"
}
]
}
},