Nope, sorry. The install for web access is tied into the install for Virtual Center Server.
From the PDF.
Installing Virtual Infrastructure Web Access
VI Web Access is automatically installed when ESX Server is installed. On
VirtualCenter Server, VI Web Access can be installed from the VirtualCenter Server
Windows setup package.
The system requirements that are mentioned in the PDF are for the client end of things.
If you found a way to separate the two it would probably not supported. If you wanted to try just for fun, then it would certainly be a challenge.