Add upsells with wp import?

Noticed I was able to export the custom field _wbs_upsells with wp export. Here is an example of what exports for a product that has 4 upsells (within the quotation marks are their product IDs): a:3:{i:0;s:5:”70720″;i:1;s:5:”88776″;i:2;s:5:”75741″;i:3;s:5:”200040″;}

I tried importing to existing products with this same format but it didn’t work. All it did was remove any upsells for the products that I tried updating.

Any idea how I can use wp import to bulk add upsells?