If you can't connect to a host because your ISP blocked the host's listening port, LimeWire will automatically try sending a PUSH request since it will assume that host is firewalled. If this host has free upload slots, it will try to open a connection to you - and if you can accept incoming connections, you won't have any problems downloading.

In case you are not accepting any incoming connections (and if you can't change that) I wouldn't use LimeWire but a gnutella client that supports HTTP or SOCKS proxy instead.