On a continuous form, if you use an unbound textbox for entry, it will retain its value. You could then update selected records to that value.
I have a form for entering medical information that uses this technique. The table it runs off of is medical requirements and it has an unbound "Date Administered' field. I then use a button to selectively add met medical requirements to an IndividualMedicalRequirement table. I am not sure if this will work in your case, but unbound controls do retain the last value entered.