Re: My view....
Gotta agree with DE727UPS on this one. As long as you're not a required crewmember, knock yourself out. HOWEVER, since you AREN'T a required crewmember, odds are a lot of insurance companies won't cover someone with low time in an aircraft like that. Hell, I have to have my MEI with me in the Seneca until I get my multi rating, even if he thinks I'm good enough to go solo. Insurance won't cover me. Another thing that may come back to bite you is when you go for the interview. "So, you've got 200 hours in a B1900? How did you get that?" Well, if you went Gulfstream it was PFT (or PFJ or whatever). Some airlines don't care, most will be polite until you leave then trash the resume. If you went through a time-building program, you're gonna get grilled. They want to make sure you were actually able to log that time legally. If it's one of those "ride along and log" time building programs, you just spent a load of $$$ for nothing.
I'm not saying EVERY time building program is bad, I'm sure there are some good ones out there. Just like most things in the aviation world, if it looks to good to be true, it probably is.