Using a 7_4 JDBC driver to connect to 8.0

Is this supported ? I have a deployed code which connects now to 7.4,
and I would like to upgrade the server to 8.0. Changing the JDBC driver
too would mean to change a lot of our code, which we can only do in a
new release, but the DB migration should happen before we can release
the new version.
I briefly tested the 7.4 driver with 8.0 server, and it seems to mostly
work except it hangs consistently in a particular operation (I was
testing our web pages). A thread dump taken after the hang shows always
the same:

        at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.read(SocketInputStream.java:129)
        at
java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
        at
java.io.BufferedInputStream.read(BufferedInputStream.java:235)
        - locked <0xec63f5c0> (a java.io.BufferedInputStream)
        at org.postgresql.core.PGStream.ReceiveChar(PGStream.java:166)
        at
org.postgresql.core.QueryExecutor.executeV3(QueryExecutor.java:127)
        - locked <0xec63e548> (a org.postgresql.core.PGStream)
        at
org.postgresql.core.QueryExecutor.execute(QueryExecutor.java:100)
        at
org.postgresql.core.QueryExecutor.execute(QueryExecutor.java:43)
        at
org.postgresql.jdbc1.AbstractJdbc1Statement.execute(AbstractJdbc1Statement.java:517)
        at
org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:50)
        at sun.reflect.GeneratedMethodAccessor13.invoke(Unknown Source)
        at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:585)
        at
org.postgresql.jdbc2.optional.PooledConnectionImpl$StatementHandler.invoke(PooledConnectionImpl.java:452)
        at $Proxy2.execute(Unknown Source)
 [...our code follows...]


Do I have any chance to make this combination (7_4 driver/8.0 server)
work fine ? If not my only chance is to stay with the 7_4 server :-/

Thanks,
Csaba.