... but i don't see any way to slow it down

I once had a similar requirement (not LWP, but X11 connections, though).  For this, I simply sent the data through a bidirectional proxy (implemented with IO::Socket and IO::Select), and inserted delays as appropriate. I.e., the inner loop shoveling the data roughly looked like this

    while($sel->can_read) {
        my $nbytes = sysread( ... );
        
        my $wait_sec = $nbytes / $bandwidth;
        select(undef,undef,undef, $wait_sec);  # delay

        syswrite( ... );
    }
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So, let's say with 10000 bytes being transferred ($nbytes), and with the simulated $bandwidth being 2000 (bytes/sec), a total delay of 5 sec. would be forced upon the transfer. This could be refined to take the real bandwidth of the connection into account (which was large in my case), but in order to just get a feel for how slow something is, it might be sufficient as it is...  Similarly, you could add roundtrip latencies, or play with transfer block sizes, etc.

Curiously, this is the topic of Flavio Poletti's article in the current issue of The Perl Review, using just the features in LWP::UserAgent.

Maybe this one?

Slick little insertion therein. ++

#!/usr/bin/perl -w

use IO::Socket; 
package IO::Socket::INET;

sub sysread { 
 my $self = shift; 
 select(undef,undef,undef,0.1); 
 $self->SUPER::sysread(@_);
}

sub syswrite { 
 my $self = shift; 
 select(undef,undef,undef,0.1); 
 $self->SUPER::syswrite(@_);
}

package main; 
# Your LWP code here... 
use LWP; 
use LWP::Debug '+'; 
print LWP::UserAgent->new->request(HTTP::Request->new(GET =>
"http://www.perl.com"))->as_string;
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