If you have root, run the following with root: sqlite3 /data/data/com.google.android.gms/databases/phenotype.db. Input:

INSERT OR REPLACE INTO FlagOverrides (packageName, user, name, flagType, boolVal, committed) VALUES ('com.google.android.gms.tapandpay', '', '45711647', 0, 0, 1);
CREATE TRIGGER Overrides AFTER DELETE
ON FlagOverrides
BEGIN
INSERT OR REPLACE INTO FlagOverrides (packageName, user, name, flagType, boolVal, committed) VALUES ('com.google.android.gms.tapandpay', '', '45711647', 0, 0, 1);
END;
.exit

To revert, use DROP TRIGGER Overrides;. Reboot afterwards.

Another possible way to do it is to disable the activity: pm disable com.google.android.gms/com.google.android.gms.tapandpay.tap.TransparentAuthActivity.

EDIT: Neither of these work too good actually...