How to calculate Green Up Stake for selection?

[Anbell]

This is most certainly a daft question but I can't find an answer.

As an example, I lay a horse twice using automation (unmatched when they hit the market but subsequently matched) for
$50 at 10.0
and
$50 at 12.0
so my exposure is
$100 @ 11 = $1000.

The horse gets to 12.0, and I effectively want to Green(ish) Up by entering a bet at 13 (approx$80), and Take SP if I don't get matched.

So my really daft question, is where can I find / store / access the $1000 value??

I don't think I can use the matched bet info to store a value, because that only has "the most recent Lay bet" - so that doesn't work here.

I can't use Net Stake ( I want to know the liability, not the stake)

I can't use P&L of a selection, because I might have laid a few horses in the race.

Thanks in advance. (I'm pretty sure I'll kick myself when I learn the answer!)

[Anbell]

re-up in case someone can help with this