Using Mongo's positional operator ($) in update mutations

Is it possible to use MongoDB's [positional operator](https://docs.mongodb.com/manual/reference/operator/update/positional/) in a generated `updateOne`/`updateMany` resolver?

For example, I would like to make an update like this (from Mongo's doc):
```
db.students.updateOne(
{ _id: 1, grades: 80 }, # Finding the 80 value in the grades array
{ $set: { "grades.$" : 82 } } # Replacing it by an 82
)
```

On my server, I've set the following generated update mutation:
```js
// ...
schemaComposer.Mutation.addFields({
studentUpdateOne: StudentTC.mongooseResolvers.updateOne(),
});
// ...
```

On my client, I've tried the following query and some others but I can't get the `$` to not generate syntax errors:
```
mutation {
studentUpdateOne(
filter: { # Filtering works OK
_id: 1,
grades: 80
},
record: { # Updating throws syntax errors
grades: { $: 82 } # I also tried ` "grades.$": 82 ` and ` grades["$"]: 82 ` with no luck
}
) {
record {
_id
grades
}
}
}
```

I am not yet very familiar with GraphQL syntax so I may be missing an easy fix.
But is it at all possible?
Thanks