It's actually very simple and can potentially have a large performance impact. For the 3.1 source I used RC1.

In case you want to do it yourself:

1) Copy the following files from the 3.1 source to your 2.1.8 source:

Code:
net/sf/hibernate/impl/ColumnNameCache.java
net/sf/hibernate/impl/ResultSetWrapper.java

2) Edit net/sf/hibernate/loader/Loader.java

Code:
913c913
<          columnNameCache = ColumnNameCache.construct( rs.getMetaData() );
---
>          columnNameCache = new ColumnNameCache( rs.getMetaData().getColumnCount() );

3) Compile.