Hi Todd,
Thank you for your interest in Syncfusion products.
You can format the cell as text by using NumberFormat. For leading Zeros you have to set the format as "00#". Please refer the below code snippet:
[C#]
sheet.Range["A1"].Number = 0001;
sheet.Range["A1"].NumberFormat = "00#";
Here is the sample for your reference:
http://websamples.syncfusion.com//samples/XlsIO.Windows/XlsIO_Cell_format/main.htmPlease try this and let me know if this helps.
Regards,
G.Yavana