The shortest answer to your question is:
Make a wrapper ActiveX of the existing one in VB.
All the parameters of the wrapper class should be defined as VARIANT.

VFP7 has strong typing, but I am not sure how strong it is.
Because I can define variable with a statement like this:

LOCAL lnTest AS Integer

and after that run a line like this:

lnTest = 'This should generate an error (according to my idea of strong typing)'

and it does not fire an error.
So I believe that (even in version 70) VFP works with VARIANT type variables.

HTH