I may be wrong but I believe you can first use fopen() (for read/write access) since fopen() attempts to open a file with exclusive access.

If fopen() fails it will return a -1 indicating the file is currently in use. If fopen returns a value > 0 you can fclose() it and immediately USE the table exclusive. Your only exposure should be during the short span between fclose() and using the table exclusive.

Although I believe this is accurate, please be sure to test this yourself.