Don't think it is possible...
So may be build more transports right from start
Thanks, that was what I thought :-( I still find it odd that you can load and transport an entire stack from Southern Sweden all across the Baltic Sea to Kronstadt in just 14 days, but you can only transport one stack across Oresund in one month. It doesn't make any sense.
Producing new naval transports is not really an option since they take 180 days to build.