They consummated the shadow marriage by wrestling on a foam pad bought for the occasion.
"We wanted to have an outlet for all our fears and trepidation, before we got to the big dress part," explained Jessica.
The couple were so convinced of the benefits that they now offer a service of premarital counselling and officiating shadow wedding ceremonies, with prices varying from US$2500 ($2875) to US$7500.
Critics will say "dark" ceremonies are just another barmy, new-ageyaddition to the US$53 billion wedding industry.
But many couples will completely understand the urge to bring back down to earth an eagerly-awaited event that can feel like a giddily-heightened pantomime.
Relationship counsellor Denise Knowles said: "I've yet to encounter a shadow wedding, but there's a definite shift towards couples designing their own vows and speeches in a much more humanistic manner, permitting more personality, humour and occasionally self-deprecation."
Today the average first-time bride is 32 and most couples have lived together for years before they say "I do".
So she knows she's not marrying Mr Perfect, and her groom doesn't expect Miss World.
At my own registry office wedding in 2010, my husband and I both wore outfits we'd seen each other wear before, because the idea of unveiling myself like a Disney princess seemed so alien to our life as a laidback couple who fell in love wearing jeans and parkas at music festivals, on camping trips and in Dalston dive bars.
"For us, the best bit of our shadow wedding came after we'd admitted all the ugly stuff about ourselves," explains Jessica.
"To hear the words 'I know all this, and I still choose you, you are still my person' is a lot more powerful than most conventional wedding vows." She has a point.
When my friends got married in Cornwall in 2009, it was an idyllic country fete affair complete with bunting and cupcakes - but the highlight for me was the bride's speech, in which she described her groom as, "the grumpiest man in the world, but Ingo, I love you".
In Jungian psychology, the shadow refers to the instinctive, irrational and least desirable aspects of one's personality; your dark side, the bits you feverishly suppress. Especially on your wedding day.
But do we really need a pricey ritual to prove that one's marriage isn't a collective delusion? As Denise says, "I'd hope these conversations would happen long before you decide to get married. If you haven't felt able to verbalise your concerns until now, perhaps you shouldn't be getting married."
However, Andrew Hinman, 36, from California, a scientist who had a shadow wedding courtesy of Jim and Jessica in 2011, describes the ritual as "a psychological insurance policy".
"I was able to address parts of me that were not on board with getting married," he says.
"It was helpful for me to have a structure, a framework for all the back-and-forth inside me. I felt totally solid about our coming together, knowing that the negative side had now been acknowledged."
Jessica tells me that not long ago, when she and Jim hit a rocky patch and she went for a soul-searching walk on the beach, "it hit me that Jim had warned me about a particular trait, and I'd vowed to accept him and work through it", she says.
"It was our shadow wedding vows that held us together - not our wedding vows."
"We're well aware shadow weddings won't be for everyone," admits Jim. "But if you're a couple of consciousness junkies like we are, then it just might be a fit."
Whether or not you decide to add a wrestling pad to your budget, it definitely seems like weddings are finally getting real.
- Independent
