Excel file on Windows client, is it possible to allow another user read-only if the file is already open?

I have a spreadsheet on a Windows 2003 R2 server. The clients are all Windows 7 using Excel 2010. If a remote user opens the spreadsheet first then any other "local" user gets access denied if they try to open the file afterwards. By "remote" I mean across a WAN link, whereas "local" means on a LAN to the server.

Is it possible to allow the file to be opened "read-only" instead of getting access denied? The spreadsheet is not configured to be shared within Excel.

This is not a permissions issue, everyone can access the file at the NTFS permissions level.

I suspect it may be to do with op locks and the fact that the remote user is across a slow link (satellite).