PPLNS (p2pool's payout method) by design discourages pool hopping, pretty successfully. While your not technically hopping, it will have the same effect for you.
PPLNS has no expected effect on reward for hopping miners.
Edit: the thread title means hopping isn't statistically expected to gain anything, but it wont lose anything either.
If you read OP you'll note he is buying large short lived mining rental contracts on p2pool, on his last big contract we/he happened to mine a very lucky block that likely paid every share he had in the chain from that rental.
While I'm enjoying our current luck, one thing I know is that it's bound to change...
Hence while he likely just had a very profitable run with our lucky block, that will not always be the case (rent multi-PH of rigs, find a block just after the rental expires).
The highest probability for the best reward is clearly to stretch out the mining to at least include 1 expected block, if not several.
P2Pool is (almost) hop-proof due to using PPLNS but does not victimise hoppers.
You CAN'T change the probability of a share being rewarded vs the amount it is rewarded.
If there are more shares in the next payout, they will be rewarded less each, but the expected number of payouts of course increases with the increase in the number of shares.
P2Pool currently has a perception problem due to the fact that only a small % of your shares get a reward.
But you can't decide which of your shares will be rewarded, that's purely based on the luck of block finding.
There's no magic memory in any pool that decides, because you found a block now, when the next one will be.
Another way to look at it would be this:
If p2pool does victimise hoppers, you could increase your expected reward by DDoSing the largest p2pool node ... ... ...
... ... ... fortunately that's not true.