The original feeder palps which come with the Haruspex kit were pulled/sawed/bitten off.
An Imperial Scion flag bearer was modified to look like he was being pulled backwards
A few structural tentacles were rolled with gardening wire inside to give them strength. These were attached to the maw. An inner mouth was constructed with plasticard and green stuff.
One of the tentacles (with wire inside) was attached to the scion to look like it is pulling him but it is actually holding him up.
More green stuff tentacles were rolled and left to partially cure so that they could be handled.
They were bent into interesting shapes and left to dry before being attached with blu-tac
The tentacles were rearranged in a pleasing manner before being permanently attached with more green stuff