I know I'm 3 1/2 years late to this party, but had been searching for a solution to this issue and found something that works. I'm highlighting web articles using Liner. When I use the EN web clipper to clip the page that contains the liner highlights, they are moved to EN and include the highlights.
Note that using Liner's built-in export function only sends the highlights to EN.
**edit with more info**
Also discovered that if you use the "Memo" function in Liner (which attaches a note to a highlight), then it stops the highlight making it over to EN when using the above technique.