Well, there is no direct way to add the hyperlink to some part of the portion and not the complete portion of text in a text frame. I have created an issue in our issue tracking system with issue id: SLIDESNET-36116 for enhancement of the feature of hyperlink to support your request. As soon as some information is shared, you will be notified via this forum thread. The workaround can be to split the portion, add the hyperlink to the required portion and add back to the paragraph in the text frame.