spinoffs in gnucash

[Stuart McGraw]

I have an accounting question about spinoffs followed by 
a "how to do" question for Gnucash.  I found some earlier 
posts but nothing that seemed very authoritative.  (And
apologies in advance if I have the terminology wrong, I
an very new at this!)

Imagine that ParentCo spins off SpinCo with 1 share of 
SpinCo stock for every 4 shares of ParentCo stock.
After the spinoff ParentCo is $25/share and SpinCo is
$20/share.  As I understand it, the calculations are:

 Spinoff ratio = 1 / 4 
 Adjusted Spinco share price = $20 * 1/4 = $5
 ParentCo + adjusted Spinco = $25 + $5 = $30
 ParentCo ratio = $25 / $30 = 5/6 
 Spinco ratio = $5 / $30 = 1/6

Assume my basis price/share for ParentCo is $18/share.
The post-spinoff ParentCo basis = $18 * 5/6 = $15/share
The Spinco basis = $18/share * 1/6 = $3/share

Now suppose I have 50 shares of ParentCo.  I should get 
12.5 shares of SpinCo but I actually get 12 shares and
.5 share * $20/share = $10 as "cash in lieu".  

My question... how do I represent this transaction in
Gnucash???

(Actually, I think I can handle the spinoff proper but
I an confused about the cash-in-lieu.  Since the SpinCo
basis is $3/share, the .5 share is only $1.50.  So that
leaves $8.50 of the cash-in-lieu as what?  Capital gains?

If someone could sketch out the transactions (with both
sides, using the numbers above), I would be immensely 
grateful!