Yes, you can. On your Confirm.php page you will need to add this field to your form:
<input type="hidden" name="discount_amount_cart" id="discount_amount_cart" value="<?php echo $eCart1->GetDiscounts(); ?>" />
You will have to change eCart to your cart name. However, this will require that you update the amount that you send to PayPal in this line of code:
<input type="hidden" name="amount_<?php echo $eCart1_Index+1; ?>" id="amount_<?php echo $eCart1_Index+1; ?>" value="<?php echo WA_eCart_FormatNumber($eCart1->DisplayInfo("Price") - (($eCart1->DisplayInfo("Price")/$eCart1->TotalColumn("TotalPrice")) * $eCart1->GetDiscounts()), false, 2) ?>" />
to something like this:
input type="hidden" name="amount_<?php echo $eCart1_Index+1; ?>" id="amount_<?php echo $eCart1_Index+1; ?>" value="<?php echo WA_eCart_FormatNumber($eCart1->DisplayInfo("Price"), false, 2) ?>" />
Again, this feature is not something that is supported in eCart, but it is something you can accomplish with some custom coding.