Unfortunately there is no way to collect your PERS benefits without paying tax on them in the year they are received. The funds from that plan would not be eligible for rollover to your TSP or to any other account.
The only time that you can roll over funds is when the funds are going from one tax deferred retirement account to another tax deferred retirement account. Your PERS pension is not a tax deferred account as your TSP plan is.
Any benefits you receive from your TSP will be taxable income to you in the year you receive them, regardless of how you reinvest the funds. However, as long as your benefit amount is not reduced by taking the payments now, you are still ahead by taking the benefits and paying the taxes which will be due.
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