Pen looks like this(you can use different colours):
Pens Needed:
1x Bic Stic Grip (same as in ZT Mod by K4S)
2x Flexgrip Ultra with metal tips
1x any grip which is longer than 3.5 cm (i used blue G2)
1x cap from RSVP
Parts:
1- tip from Flexgripa
2- shortened body from Flexgripa
3- this parts from Bic Stic Grip which connect bodies
4- body from Flexgripa
5- spring from Flexgripa
6- grip G2
7- clicker without clip from Flexgripa
8- cap RSVP
9- extended ink tube from Flexgrip
Tutorial:
1. First we take one body from Flexgrip and cut it when there's a last pit from the tip
2. From Bic Stic Grip we take the part holding therefill and cut it in this place:
http://i47.tinypic.com/2duidsm.jpg
3. Connect the shortened body by the part from point 2 to the second one and screw down the metal tip of Flexgrip along with a spring to the shortened one.
4. Put a grip on a front (it's important that it's longer that 3,5cm so it could cover the link)
5. Extend the ink tube from Flexgrip with some other ink tube the same length as the cut body (around 2,8cm), connecting both ink tubes f.e. with a toothpick. Put the extended ink tube to the body.
6. Now the back - cut off the clip from a Flexgrip's clicker using a knife so it looks like this:
http://i47.tinypic.com/nvp5s7.jpg
7. Screw shortened clicker to the end of the body.
8. Put some plasticine to the RSVP cap to give the pen some balance. Then put the cap on a clicker.
Length: my - 20cm
COG: it depends on how much plasticine would you take into RSVP cap
Believe me! this pen ROCKS!!!
Enjoy!
PS: for inspiration thanks to Kanonier!!!
my is only prototype 
