Many thanks for the "swift" reply to my Q about whereabouts of Xootr site. Hope it comes back soon. While I'm online tonight, here's a pic of my upper rack mounting on an aluminium Swift. (I think I figured out how to attach a .jpeg so I hope everyone else can see it)
Comments invited about what is wrong with this idea.
swiftrack.jpg
I can think of possibility of ripping the clamp ears right off the frame. Rack is a Topeak Super Tourist that I had in parts box and as presently mounted it feels very solid. Top clamp bolt is a Dimension 50mm. Bottom one clamping the rack stays is Q/R as supplied with frameset. My emphasis is on packability rather than regular folding so I went for security of clamp bolts on top seatpost clamp and stem. One of my few beefs with the Swift is the scarcity of braze-ons (TIG-ons?) for bottle cages and racks.
Another idea is to machine an alloy collar to go around seat post and bolt the rack stays to that.

Peter
Australia

Swift aluminium folder with mix of new and junk-box parts.
SRAM 3x9 Dual Drive
Shimano Deore Octalink triple crankset.
Single 42t front ring in middle position.
Left hand SRAM twist shift
Right hand Shimano 9sp trigger
BBB alloy butterfly bar. Brooks leather bartape.
Shimano 105 rear der.
Velocity Aeroheat 406 rims.
DT Swiss 14 straight gauge spokes.
Front Shimano Deore 36h hub
Schwalbe Marathon Plus tyres
Tektro V-brakes and levers.
Brooks B17 narrow saddle.