BOVW - Combine vocabularies
I also found an interesting paper (with code) where they merged local and global descriptors.

Scene Recognition by Combining Local and Global Image Descriptors

According to the paper: They take the daisy features (local features), cluster the features into k clusters, then create a histogram with k bins. They normalize the histogram, once they do this they concatenate this vector (the histogram) with the normalized HOG vector (global features). So in the end we just cluster the local features and create histogram, then just concat with global vector and there we have a training sample.

Also there may be an alternate method where you just use local features to cluster: https://www.quora.com/How-do-I-merge-features-from-different-feature-extractors-i-e-color-histogram-and-SIFT-for-bag-of-visual-words#