The IEEE 802.15.3 MAC enables high-rate communications between devices in a wireless personal area network and has good support for applications requiring quality of service (QoS). To meet applications' QoS requirements, such as delay and jitter, the channel time allocation (CTA) scheduler plays an important role in sizing and positioning CTAs within each super-frame. In this paper, we first present a novel CTA sharing protocol, called VBR-MCTA that enables the sharing of CTAs belonging to streams with the same group identity. This allows our protocol to exploit the statistical characteristics of variable bit rate (VBR) streams by giving unused time units to a How that requires peak rate allocation. We then present two optimizations to VBR-MCTA, namely VBR-Blind and VBR-TokenBus. The former, by giving ownership of a CTA in a round-robin manner without consideration to traffic profiles, does not consume any valuable "air-time" with signaling overheads. The latter allows a CTA to be shared by multiple devices that take turns owning unused "air-time" from CTAs. We have simulated VBR-MCTA and its optimizations in the ns-2 simulator over an implementation of the IEEE 802.15.3 MAC. Our results show that VBR-TokenBus has the best delay and jitter as it provides a one to six milliseconds reduction in both compared to standard CTA methods. VSR-Blind, although having performing poorer than MCTA-Token or VBR-MCTA, is still significantly better than traditional CTA methods at a reduced overhead.