I put this line in my custom report. It's not exactly what you wanted, but it's enough for me to see if I'm on my way. Generally, if I'm off the pre-boil, I'm off the same amount at the end, and progress is usually linear. I decide along the way whether to boil longer or add DME or sugar to reach the target OG, depending on the gap.
---BOIL PROCESS-----------------------------
Est Pre_Boil Gravity: 1.050 Est OG: 1.059 SG
Boil Ingredients
Boil Amount Item Type
60 min 0.50 oz First Gold [9.50 %] (60 min) Hops
25 min 0.50 oz Fuggles [4.50 %] (25 min) Hops