Slingsby,
What you described is not uncommon, normally my technique is to advise the pilot that if they get the airport in sight we can switch to the visual approach (traffic permitting). As someone else mentioned, if we are advertising the visual approach I have absolutely no problem with a pilot requesting an instrument approach, especially if the final has the sun in their eyes making seeing the runway challanging.
Remember, SAFETY FIRST!
Mike
NATCA FWA