dhclient: lease renewal woes

[Mr Dash Four]

I have a bit of a conundrum which is causing me a few problems and I am 
hoping that any of you might be able to help me with: I am using 
dhclient to get a lease from my provider via a cable modem. When I 
acquire a new lease the following sequence occurs:

1. dhclient broadcasts DHCPREQUEST on 255.255.255.255;
2. my cable modem (which has a private IP address) responds and offers a 
lease;
3. dhclient then accepts the lease and records it in the .leases file.

So far so good, but the .leases file has "option dhcp-server-identifier" 
which points to an external dhcp server (with public IP address in it, 
say 82.x.x.x). When a time comes and dhclient needs to renew the lease 
it tries to contact this 82.x.x.x address. The problem with this 
approach is that my provider's DHCP server doesn't respond to direct 
queries and they get ignored.

So, is there a way to "force" dhclient to always use a broadcast 
(255.255.255.255) in order to renew the lease instead of contacting the 
IP address specified in the dhcp-server-identifier field in the .leases 
file directly?

That way, when the lease needs to be renewed dhclient will start with a 
broadcast DHCPREQUEST, then my cable modem (with its private IP address) 
will respond to that request and the lease will be renewed swiftly as in 
the above sequence?

As it stands though, when the lease renewal comes about, my dhclient 
becomes "stuck" and I have to restart it. I am also not sure if I 
"manually" intervene and alter the dhcp-server-identifier to point to 
255.255.255.255 would help either. Many thanks in advance for any help 
and advice given.