Did you ever get anywhere with this? The only thing that I found was from the old forum:

http://forumsarchive.laravel.io/viewtopic.php?id=2643

Basically doing a raw statement like you said.

I worked with the same issue. You can put the following method on your Model.

public function insertUpdate(array $attributes)
{
    $this->fill($attributes);
    
    if ($this->usesTimestamps()) {
        $this->updateTimestamps();
    }

    $attributes = $this->getAttributes();

    $query = $this->newBaseQueryBuilder();
    $processor = $query->getProcessor();
    $grammar = $query->getGrammar();

    $table = $grammar->wrapTable($this->getTable());
    $keyName = $this->getKeyName();
    $columns = $grammar->columnize(array_keys($attributes));
    $insertValues = $grammar->parameterize($attributes);

    $updateValues = [];

    if ($this->primaryKey !== null) {
        $updateValues[] = "{$grammar->wrap($keyName)} = LAST_INSERT_ID({$keyName})";
    }

    foreach ($attributes as $k => $v) {
        $updateValues[] = sprintf("%s = '%s'", $grammar->wrap($k), $v);
    }

    $updateValues = join(',', $updateValues);

    $sql = "insert into {$table} ({$columns}) values ({$insertValues}) on duplicate key update {$updateValues}";

    $id = $processor->processInsertGetId($query, $sql, array_values($attributes));

    $this->setAttribute($keyName, $id);

    return $this;
}