You can do this only to a very limited extend. The easiest way would be not to number those two footnotes, but to use any character as footnote symbol. Then you could choose the same character for both footnotes. You could even use a number as manually-assigned character, but then the trouble starts if there are more, numbered footnotes in the same document. Because then, you have to take care not to get three footnotes with the same number (two manually-assigned and on auto-numbered).
Personally, i would recommend not to use same numbers for two footnotes, but to use cross-references. You can cross-reference both the footnote number and the page where that footnote is located. So, in your case i would insert two "standard" footnotes with different numbering, and put a textual cross-reference in the second one: "
See footnote <number> at page <page-number>."