I love lupine so I feel your pain. I often cut mine back pretty drastically because they look ratty by late July. They never seem to mind and they bounce back with vigor. So I think you can go for it with the trimming.

Are nearby ants helping to cause the aphid infestation? If so, you might try using a nontoxic borax ant trap to control the ants.

ants milk aphids.... for the honeydew ...

they do not cause the aphids.. nor do they spread the aphids ..

get rid of the aphids ... and the ants will mind their own business .....

there is little point in trying to control ants... and i am NOT talking about the down south man eating ants ... lol ..

now.. if they come in my house.. its all out warfare ... or undermining the cracks in my asphalt ....

ken

IDK Ken, I have definitely reduced the aphids in my greenhouse by trapping the ants. I have also reduced aphids dramatically by putting plants that aphids love in a place where the ants have a harder time reaching them (by suspending windowboxes from chains). So my observations tell me that ants do make aphid problems worse.

I frankly (for no reason other than instinct) believe that ants transport aphids to plants as much as sheep farmers transport sheep to new pastures.
Other articles on the web support this..I'll link one.

Here is a link that might be useful: Col State, ants and aphids