the current PI SDK (1.3.x) does not support buffering.
According to our Engineering Plan, this feature (PI SDK Buffered Writes) is slated for PI SDK 1.4.0, planned for 1Q2010. For now, depending on the nature of your project, you could consider using PI Advanced Computing Engine (ACE) to take advantage its out-of-the-box connection management and buffering capabilities.
The PI ACE install kit is available as part of the vCampus PI Products Kit you probably downloaded from the vCampus Download Center. You can find its documentation on the vCampus Library and a discussion forum is dedicated to that product.