In reply to ndesch:
You can use the uvm_config_db() in the pre_randomize() function of your sequence. Use m_sequencer as the context for the get().
function void pre_randomize();
if (cfg == null) begin
if (!uvm_config_db#(my_config)::get(m_sequencer, "", "cfg", cfg)) begin
`uvm_error("NOCFG", "No config object available");
end
end
endfunction