chained throatseeker, blighted agent, proliferating spells.  Is there enough infect in U?  Obviously can splash if needed, but blue's great for unblockability.  Add curiosity, infiltrator's magemark maybe.  Ichorclaw myr.

Just do another search for infect in exclusively blue or colorless.  There are good choices, but not so many that it's hard to pick.  Look for proliferate, too.

clockspinning (not quite proliferate, but maybe useful