Adding filters/anchors on-the-fly

Hello,

I am wondering if it is possible to add filters/anchors with pfctl to a 
running instance of pf?

I have put an anchor option in my pf.conf, and I can add tables and 
filter rules to that OK. But suppose I had no anchor option in pf.conf; 
is there some way to add one with pfctl and insert rules and have them 
used? If so, I have not been able to figure it out. This as not critical 
by any means as it does work fine otherwise, but I am just trying to 
figure out if I am missing something, or it just doesn't work that way.

Thanks.