There is a roundabout way (actually a tax loop hole) of doing what you want to do. You can "rollover"* the savings bonds to a 529 plan. You open a 529 plan for yourself (naming yourself as beneficiary is allowed by most plans). Then later, you transfer (rollover) the plan to another 529 where your niece would be the beneficiary. Transfers of 529 plan beneficiarys, to other family members, is allowed. Check your 529 plan rules before doing this as some of them may have age limits.
For some back ground info see: http://www.fastweb.com/financial-aid/articles/how-do-i-roll-over-us-savings-bonds-into-a-529-college...
*You actually cash in the bonds. Then deposit the entire proceeds into a 529 plan.
