Clustering and captcha/CFFILESERVLET mappings

While testing clustering, I realized that each ColdFusion instance will write CFIMAGE temporary files to its own ./tmpCache/\CFFileServlet path. The issue is that CFFILESERVLET gets a mapping (alias, virtual directory) in the webserver to one folder. If I have two ColdFusion instances setup on a cluster, within the same server, the image is generated and stored in one of the two instance installation folders. There is a 50/50 chance that the file is stored in the folder that isn't mapped in the web server configuration.

Is there a "proper" way to handle this, when using two ColdFusion instances installed on the same physical server?