How to prevent session timeouts in Punchout

I do hope that someone can help me.

We have a user who believes the 30 minute session timeout is insufficient for him to shop in a supplier site. He had spent 90mins getting his shopping trolley finalised and when he exited from the supplier site to E business suite he lost all of it.

Apart from changing the ICX:Session timeout what else would I need to do to prevent this from happening?

Also do you know of any side effects/issues experienced by increasing this time limit.

I read on metalink that memory leakage and JVM's running out of memory was a possibility.