IK-chain tipfix

Hello,

is there a possibility within an IK chain to
assign a new position to individual links to fix them in place.
I need it to fix the last bone (fingertip) which is already part of the IK-setup !

see gif! when blendweight is set to one it stays to the center of the green circle which is an child of the white square (the ik-ctrl)

ik_pin