I came up with the same idea with yours. However, when I do it, I found a problem.
If an exon is the first exon of a gene, then there is no 5' splice site , if an exon is the last exon of a gene, then there is no 3' splice site. So many extended in both directions could be wrong.
I want to know if there is any suggestions to solve this.
Thank you in advance.