Why not have a custom kydex holster made?
Checked safariland's website holsters.com? I think I recall seeing holsters for 1911 with rail.
ETA: I found several by googling: 1911 rail holster
I Just noticed the Blackhawk Serpa CQC 1911 holster specifies "with or without rail"
Cameramonkey, the Sig 1911 has a non-standard slide profile. The difficulty in finding a holster is very real-- most 1911 holsters won't fit the Sig, even if they are designed to carry a railed 1911 holster. Unless it's a holster made specifically for the Sig, it's probably a no go. Jerry45Acp, Hooch Holsters and Mills Tactical would both be fine options for you to check out. Since Rings doesn't seem to have produced a Blue Gun of the Sig 1911 yet, whoever makes the holster will have to have you bring it to their shop in person and wait while they holster is made.
Thanks. I Forgot about Blackhawk. But it seems their 1911 Serpa holsters are not full length. I really don't want the end of my pistol sticking out of the holster. I would hate to damage the front sight.....I might need it.
Check out the Raven Concealment Phantom holsters.