In the latter part of this summer I applied the auxin alpha naphthalene acetamide to my flowers right after pollination.
The table that contains this information is at:
http://spreadsheets.google.com/ccc?key=pxHhTw7ylg782w9GDTC48Sg&hl=en
As an example, for #217 (Calocarpa X Nutkana) I have listed 2 crosses with Carefree Sunshine. The first was a normal early season cross (6/17/2007). The second used hormone and was pollinated on 8/10/2007.
The full paper linked to below looked at the effect on peaches. It will be interesting to see if the application of auxin allows those in northern climates to extend their pollination season further into the summer.