Pass user built json encoder into Flask's jsonify

I want to pass a numpy JSON serializer I wrote into Flask's jsonify function, but I cannot find a way to do this. I cannot use json.dumps, because I have to set the status_code of the Flask response when handling an error message. Is there a way to pass the JSON serializer in as a parameter, similar to using the cls parameter in json.dumps as shown here: Convert numpy type to python? My code is below; thanks.

import json
import numpy as np
from flask import Flask, jsonify

class JSON_Improved(json.JSONEncoder):
    '''
    Used to help jsonify numpy arrays or lists that contain numpy data types.
    '''
    def default(self, obj):
        if isinstance(obj, np.integer):
            return int(obj)
        elif isinstance(obj, np.floating):
            return float(obj)
        elif isinstance(obj, np.ndarray):
            return obj.tolist()
        else:
            return super(MyEncoder, self).default(obj)

app = Flask(__name__)
@app.errorhandler(ErrorMessage)
def handle_invalid_usage(error):
    response = jsonify(error.to_dict())
    response.status_code = error.status_code
    return response