It looks like Global Temporary Tables are available properly in Sybase 16 SP02 PL04 HF1.
Essentially, these look like a normal table but the data is only visible in a session.
see https://archive.sap.com/discussions/thread/3928146
under the covers, you create a temp table and it creates proc at the same time with the name of the table with a _<objectid>.
Inserting into the global temp table then creates a temp table.
All really good - but no documentation on it.
Why no documentation ?