You could either have *ROOT* ** *ROOT*
(where the asterisks on the root would find affixes) or you could simply have ROOT ** ROOT
(and define the affixes in the Word Prefix and Suffix menu)
Note that the guide for editing a term points out that you should have the two asterisks together to represent any number of intervening words. If you only have the possibility of two intervening words you would use a space between the asterisks.