As far as I know it is not possible to have the srt subtitles at the top because they contain only text and no position information. If your player supports them you should use the .sub files instead.
Two and a half years later, I’d like to point out that there is a way to show subtitles moved to the top via the extended command {\an8}:
1
00:00:05,000 --> 00:00:08,000
{\an8}Top-center alignment