The only way I know to stop a recalculation while keeping the graph visible is to Detach the object. You can do this from the front end by right clicking the object and clicking Detach. The detach state is not saved or persisted when you close the document, so the object will be re-attached. Perhaps a macro could do detach/attach an object?
I am not sure if this will work for you but you might try using Set analysis and ignore certain selections but this might of course cause problem if you at sometime during your analysis actually want to calculate based on "ignored" selections. You can also set conditions on the actual expressions as well as on the whole graph. Check out "Whats new in QV11" for an example of this, the "select metric" on the dashboard controls what expressions to calculate in the actual graphs.