"Catch as catch can" is an idiom used to describe the act of doing something in an impromptu or haphazard way. Some synonyms that can be used for this expression are doing something in a "make-shift" or "ad-lib" manner. Other similar expressions include "fly by the seat of your pants," "wing it," and "make do." All of these expressions suggest a sense of unpredictability and lack of planning, and they are often used to describe situations where someone is improvising or taking on a task without much preparation. Overall, there are several synonyms for "catch as catch can," each of which conveys a similar sense of spontaneity and adaptability.