How to make specialization of `boost::mpl::sequence_tag` when only trait available?

I have no problems when i know template of type, that will be passed into `boost::mpl::sequence_tag`:
```
namespace boost { namespace mpl
{
template
struct sequence_tag;

template
struct sequence_tag>
{
typedef fusion::fusion_sequence_tag type;
};
}}
```

But my case is when have no access for `std::tuple` template and i only have an `is_tuple` trait:
```
namespace boost { namespace mpl
{
template
struct sequence_tag;

template
struct sequence_tag::value>> // won't work
{
typedef fusion::fusion_sequence_tag type;
};
}}
```

SFINAE is not working on `boost::mpl::sequence_tag`, does it have an another way?