Possible Clues:

• Cousins tiling houses impress
• Implant's not extracted yet, rumour has it
• Impress what could be still inside
• Plant the idea that there's one sign of learning at the institute
• Plant idea establishing isn't in Illinois
• Introduce gradually some plain Stilton
• Introduce gradually in new list
• Put imagination into slit in dress!
• Introduce trendy source of booze — only one left
• Gradually establish in someone’s mind