VMware tools upgrade suggestion needed after upgrading ESX host

Hi,

We have around 350 ESXi host and 4000 VMs sitting accross diffrent cluster.We are upgrading from ESX4.1 to ESXi 4.1 and each host having 60 -100 VMs.Once the host is upgraded to ESXi 4.1 but VMs is still having old vmware tools and old Virtual hardware version.Is any method of upgrading vmware

tools automatically rather than manually each VMs by setting rule because we cant get down time for all VMs at same time.If any info missed then let me know.

Any suggestion on this will be appreciated.

thanks

vmguy