The most likely solution is to rewrite the MSOGenerateExcelFile activity to try to get Excel to format the values as numbers. Just try below.
1) Create a new function called getScalarPropertyType to inspect the data type of the property being exported. If the datatype is integer it returns true, otherwise false.
2) Create a copy of the DCOXLGenerateZipEntryMap function, called XLGenerateZipEntryMap. There are two main areas within the function where the above check needs to be inserted
2.1 When the numeric property is used by itself: Row 134 to 164 of DCOXLGenerateZipEntryMap. The new logic commences at line 112 to 155 in the new XLGenerateZipEntryMap function.
2.2 When the numeric property appears within an array (pagelist) property: Row 194 to 276 of DCOXLGenerateZipEntryMap. The new logic commences at line 180 to 225 in the new XLGenerateZipEntryMap function.
3) Create a copy of the @baseclass.MSOGenerateExcelFile activity. Reference the new function, XLGenerateZipEntryMap, instead of the DCOXLGenerateZipEntryMap in step 4's Java logic.