Server does not recognize boundary with quotes in multipart/form-data sent from SoapUI

Hi.

SoapUI generates post-request:

Content-Type: multipart/form-data; boundary="----=_Part_8_463918295.1476087034092"

...

------=_Part_8_463918295.1476087034092
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: form-data; name="session-id"

...  

If boundary without < "" , = > then server recognize request:

boundary=---------------------------7e02701a11f0342

If boundary with ["" , =] (as in SoapUI) server doesn't recognize request:

boundary="----=_Part_8_463918295.1476087034092"

The programmers will not fix it on server. So I can not write the testcase.(

Can I set custom boundary in post-request multipart/form-data? Maybe I can do it from groovy script test step?

Who can help me?

Thanks.

Regards, S.K.