Do you have in mind something like 0.9 * 1000/9 + 0.1 * 100/1 = 110? This doesn't look right

This can be justified by change of rules: deciders get their part of total sum (to donate it of course). Then expected personal gain before:

for "yea": 0.5*(0.9*1000/9+0.1*0)+0.5*(0.9*0+0.1*100/1)=55 for "nay": 0.5*(0.9*700/9+0.1*0)+0.5*(0.9*0+0.1*700/1)=70

Expected personal gain for decider:

for "yea": 0.9*1000/9+0.1*100/1=110
for "nay": 0.9*700/9+0.1*700/1=140

Edit: corrected error in value of first expected benefit.

Edit: Hm, it is possible to reformulate Newcomb's problem in similar fashion. One of subjects (A) is asked whether ze chooses one box or two boxes, another subject (B) is presented with two boxes with content per A's choice. If they make identical decision, then they have what they choose, otherwise they get nothing.