One workaround would be to do it via the pricelists menu as there you can do a mass-import. You can create a menu based on the model product.pricelist .item model.: to do so, go to "model"  find the model I mentioned and then go the bottom of the page, you will see a button "create a menu ". Create a menu and put it wherever you want. (You can still delete it after by going to the model "menu items"). Once it is created you can export and import fields related to the pricelist and in this specific case you would need 

1) the product.pricelist.item external  ID 

2)  the  product  template  external  ID 

3)  the   pricelist  ID 

4)  Applied  on (probably product variant in your case) 

5)  product  variant  ID  (product.product) 

6)  compute  price

7)  Percent  Price  (if you wan to do it using a percentage of the base price) 

 You should import those fields in the model I mentioned right above and this will actually create the lines in your pricelist. 

Hope this helps ! 

NB : If you don't find the menu's I'm talking about use the rapid search bar on the main dashboard, only typing the words.