Can I have Last Purchase Price ignore certain orders?

On an item record, I want to utilize the 'last purchase price' field to automate the 'purchase price' of our items. However, once we purchase the items from vendors we then sell them intercompany to our subsidiaries with a markup and after testing I've found that an intercompany order will also change the last purchase price to that marked up value.

Is there a way to make the last purchase price ignore certain transactions? In this case any that come from certain vendors (our subsidiaries) or if they're marked as intercompany.

I noticed that if our subsidiary MPCN purchases the item for say $2000. This will update the item records last purchase price. But if I build a PO for MPUK to purchase the item, the last purchase price line item field on that PO is still the last purchase price that MPUK purchased it for and not the $2000 rate. Is this perhaps accessible somehow?