SMCD3G w/1 static - ok to combine routable static & internal 10.1.10.x devices?

I'm in the process of moving my personal email server from 1 comcast business connection to another. Both sites use the SMCD3G. Normally, the mail server is configured directly with a static IP. However, I have noticed that, if i set it (or a router, or any device really) to an internal address within the same subnet as the SMC's ethernet interface (10.1.10.x) and a default gateway of 10.1.10.1, it appears on the internet to have my comcast-provided gateway IP as its source address. This seems beneficial to me; what I am planning is to have the mail server take the single static IP at the new site, and the router for the rest of the users on the network there configured with a WAN address of 10.1.10.2, with default gateway of 10.1.10.1. This way, all the users traffic will appear to be on the comcast gateway IP, and the mail server will appear to be on the "official" usable static given by comcast.

Would this be a supported and/or ideal configuration?