I finally get the subtitle on the timeline (I did change the speed since I wrote my title based on .mov file which ends up longer than FCP file - don't know why), but it won't let me render it. At first it started rendering, saying it is going to take a couple of hours, then the pop up window disappears, with file unrendered. When I try to render again, it just flashes.
Download my TitleExchange package.
It includes an app called gRender (free).
Export your subtitle only timeline as XML.
Then import into gRender. The app will create a new XML, an EDL and some more files.
Open the newly created XML in FCP and render out the sequence as image sequence (with alpha). It's a fast action.
Open the EDL in FCP and reconnect the images.
Though it sounds complicated – it's not.
The rendered subtitles require way less memory compared to the "generator version".