Automatically Append New Blank Row/Line/Record in Subform (Bounded Form)

Hi,

I designed a Hospital Billing System. Its working fine but during the developmentof this project I faced a problem which I also posted on this Newsgroup, however couldn't get any solution. The scenario is as follows:
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SCENARIO:

Main & SubForms are bound to tables with 1 to Many relationship.This Form (Subform) records SERVICES rendered on One Voucher. On a single voucher 1 or more services may be rendered.

Now User Input Voucher # in Main Form with Date and after filling other field on main form User records MULTIPLE SERVICES RENDERED in Subform. As the user press any Single Key in first record of Subform A NEW BLANK Record/Line/Row is Appended in the subform.
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I know that this is DEFAULT behavior of MS ACCESS table. But I want to bypass this behavior. IN SUBFORMS Pressing any key SHOULD NOT APPEND NEW BLANK RECORD in subform. New Row/Line/Record SHOULD ONLY be appended when user press any specific button.

Hope I will get a reply with sample code.

Thanks

SYED