And if your bugsmasher does not run to checklists for loss of ASI, just remember that a known power setting for a known attitude will produce known performance for a given configuration. You already know this for your aircraft - right?
If the ASI is still out on final approach, add GPS ground-speed into your scan for a rough idea of IAS. You can guess the wind effect and unless you are at high elevations ignore the difference between TAS and IAS because at bugsmasher approach speeds near sea level they are not that far apart.
This is probably a question outside the scope of a normal I.R. renewal, but a very good one. Far more use than knowing the lobe frequencies of the ILS.